I'm working on modernizing Rosetta Code's infrastructure. Starting with communications. Please accept this time-limited open invite to RC's Slack.. --Michael Mol (talk) 20:59, 30 May 2020 (UTC)

Abelian sandpile model

From Rosetta Code
Task
Abelian sandpile model
You are encouraged to solve this task according to the task description, using any language you may know.
This page uses content from Wikipedia. The original article was at Abelian sandpile model. The list of authors can be seen in the page history. As with Rosetta Code, the text of Wikipedia is available under the GNU FDL. (See links for details on variance)


Implement the Abelian sandpile model also known as Bak–Tang–Wiesenfeld model. Its history, mathematical definition and properties can be found under its wikipedia article.

The task requires the creation of a 2D grid of arbitrary size on which "piles of sand" can be placed. Any "pile" that has 4 or more sand particles on it collapses, resulting in four particles being subtracted from the pile and distributed among its neighbors.

It is recommended to display the output in some kind of image format, as terminal emulators are usually too small to display images larger than a few dozen characters tall. As an example of how to accomplish this, see the Bitmap/Write a PPM file task.
Examples up to 2^30, wow!
javascript running on web
Examples:

0 0 0 0 0    0 0 0 0 0
0 0 0 0 0    0 0 1 0 0
0 0 4 0 0 -> 0 1 0 1 0
0 0 0 0 0    0 0 1 0 0
0 0 0 0 0    0 0 0 0 0

0 0 0 0 0    0 0 0 0 0
0 0 0 0 0    0 0 1 0 0
0 0 6 0 0 -> 0 1 2 1 0
0 0 0 0 0    0 0 1 0 0
0 0 0 0 0    0 0 0 0 0

0  0 0  0  0    0 0 1 0 0
0  0 0  0  0    0 2 1 2 0
0  0 16 0  0 -> 1 1 0 1 1
0  0 0  0  0    0 2 1 2 0
0  0 0  0  0    0 0 1 0 0

C[edit]

Writes out the initial and final sand piles to the console and the final sand pile to a PPM file.

 
#include<stdlib.h>
#include<string.h>
#include<stdio.h>
 
int main(int argc, char** argv)
{
int i,j,sandPileEdge, centerPileHeight, processAgain = 1,top,down,left,right;
int** sandPile;
char* fileName;
static unsigned char colour[3];
 
if(argc!=3){
printf("Usage: %s <Sand pile side> <Center pile height>",argv[0]);
return 0;
}
 
sandPileEdge = atoi(argv[1]);
centerPileHeight = atoi(argv[2]);
 
if(sandPileEdge<=0 || centerPileHeight<=0){
printf("Sand pile and center pile dimensions must be positive integers.");
return 0;
}
 
sandPile = (int**)malloc(sandPileEdge * sizeof(int*));
 
for(i=0;i<sandPileEdge;i++){
sandPile[i] = (int*)calloc(sandPileEdge,sizeof(int));
}
 
sandPile[sandPileEdge/2][sandPileEdge/2] = centerPileHeight;
 
printf("Initial sand pile :\n\n");
 
for(i=0;i<sandPileEdge;i++){
for(j=0;j<sandPileEdge;j++){
printf("%3d",sandPile[i][j]);
}
printf("\n");
}
 
while(processAgain == 1){
 
processAgain = 0;
top = 0;
down = 0;
left = 0;
right = 0;
 
for(i=0;i<sandPileEdge;i++){
for(j=0;j<sandPileEdge;j++){
if(sandPile[i][j]>=4){
if(i-1>=0){
top = 1;
sandPile[i-1][j]+=1;
if(sandPile[i-1][j]>=4)
processAgain = 1;
}
if(i+1<sandPileEdge){
down = 1;
sandPile[i+1][j]+=1;
if(sandPile[i+1][j]>=4)
processAgain = 1;
}
if(j-1>=0){
left = 1;
sandPile[i][j-1]+=1;
if(sandPile[i][j-1]>=4)
processAgain = 1;
}
if(j+1<sandPileEdge){
right = 1;
sandPile[i][j+1]+=1;
if(sandPile[i][j+1]>=4)
processAgain = 1;
}
sandPile[i][j] -= (top + down + left + right);
if(sandPile[i][j]>=4)
processAgain = 1;
}
}
}
}
 
printf("Final sand pile : \n\n");
 
for(i=0;i<sandPileEdge;i++){
for(j=0;j<sandPileEdge;j++){
printf("%3d",sandPile[i][j]);
}
printf("\n");
}
 
fileName = (char*)malloc((strlen(argv[1]) + strlen(argv[2]) + 23)*sizeof(char));
 
strcpy(fileName,"Final_Sand_Pile_");
strcat(fileName,argv[1]);
strcat(fileName,"_");
strcat(fileName,argv[2]);
strcat(fileName,".ppm");
 
FILE *fp = fopen(fileName,"wb");
 
fprintf(fp,"P6\n%d %d\n255\n",sandPileEdge,sandPileEdge);
 
for(i=0;i<sandPileEdge;i++){
for(j=0;j<sandPileEdge;j++){
colour[0] = (sandPile[i][j] + i)%256;
colour[1] = (sandPile[i][j] + j)%256;
colour[2] = (sandPile[i][j] + i*j)%256;
fwrite(colour,1,3,fp);
}
}
 
fclose(fp);
 
printf("\nImage file written to %s\n",fileName);
 
return 0;
}
 

Console output :

[email protected]:~/doodles$ ./a.out 10 64
Initial sand pile :

  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0 64  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
Final sand pile :

  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  0  0  0  0  0  0
  0  0  0  0  1  2  1  0  0  0
  0  0  0  2  2  2  2  2  0  0
  0  0  1  2  2  2  2  2  1  0
  0  0  2  2  2  0  2  2  2  0
  0  0  1  2  2  2  2  2  1  0
  0  0  0  2  2  2  2  2  0  0
  0  0  0  0  1  2  1  0  0  0
  0  0  0  0  0  0  0  0  0  0

Image file written to Final_Sand_Pile_10_64.ppm

C++[edit]

Works with: g++ version 9.2.0 20061115
Library: xtensor
Library: xtensor-io


#include <iostream>
#include "xtensor/xarray.hpp"
#include "xtensor/xio.hpp"
#include "xtensor-io/ximage.hpp"
 
xt::xarray<int> init_grid (unsigned long x_dim, unsigned long y_dim)
{
xt::xarray<int>::shape_type shape = { x_dim, y_dim };
xt::xarray<int> grid(shape);
 
grid(x_dim/2, y_dim/2) = 64000;
 
return grid;
}
 
int print_grid(xt::xarray<int>& grid)
{
// for output to the terminal uncomment next line
// only makes sense for small grid < 32x32;
// std::cout << grid << std::endl << std::endl;
 
// output result to an image
xt::dump_image("grid.jpg", grid);
 
return 0;
}
 
bool iterate_grid(xt::xarray<int>& grid, const unsigned long& x_dim, const unsigned long& y_dim)
{
bool changed = false;
 
for (unsigned long i=0; i < x_dim; ++i)
{
for (unsigned long j=0; j < y_dim; ++j)
{
if ( grid(i, j) >= 4 )
{
grid(i, j) -= 4;
changed = true;
try
{
grid.at(i-1, j) += 1;
grid.at(i+1, j) += 1;
grid.at(i, j-1) += 1;
grid.at(i, j+1) += 1;
}
catch (const std::out_of_range& oor)
{
}
}
}
}
 
return changed;
}
 
int main(int argc, char* argv[])
{
const unsigned long x_dim { 200 };
const unsigned long y_dim { 200 };
 
xt::xarray<int> grid = init_grid(x_dim, y_dim);
bool changed { true };
 
iterate_grid(grid, x_dim, y_dim);
 
while (changed == true)
{
changed = iterate_grid(grid, x_dim, y_dim);
}
print_grid(grid);
 
return 0;
}

Compile with following CMakeList.txt:

cmake_minimum_required(VERSION 3.1)
project(abelian_sandpile)
 
find_package(xtl REQUIRED)
find_package(xtensor REQUIRED)
# if xtensor was built with xsimd support:
# find_package(xsimd REQUIRED)
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fopenmp")
include_directories(/usr/include/OpenImageIO)
find_library(OIIO "OpenImageIO")
 
add_executable(abelian_sandpile src/abelian_sandpile.cpp)
 
target_compile_options(abelian_sandpile PRIVATE -march=native -std=c++14)
target_link_libraries(abelian_sandpile xtensor ${OIIO})

Delphi[edit]

Translation of: Python
 
program Abelian_sandpile_model;
 
{$APPTYPE CONSOLE}
 
{$R *.res}
 
uses
System.SysUtils,
Vcl.Graphics,
System.Classes;
 
type
TGrid = array of array of Integer;
 
function Iterate(var Grid: TGrid): Boolean;
var
changed: Boolean;
i: Integer;
j: Integer;
val: Integer;
Alength: Integer;
begin
Alength := length(Grid);
changed := False;
 
for i := 0 to High(Grid) do
for j := 0 to High(Grid[0]) do
begin
val := Grid[i, j];
if val > 3 then
begin
Grid[i, j] := Grid[i, j] - 4;
 
if i > 0 then
Grid[i - 1, j] := Grid[i - 1, j] + 1;
 
if i < Alength - 1 then
Grid[i + 1, j] := Grid[i + 1, j] + 1;
 
if j > 0 then
Grid[i, j - 1] := Grid[i, j - 1] + 1;
 
if j < Alength - 1 then
Grid[i, j + 1] := Grid[i, j + 1] + 1;
changed := True;
end;
end;
Result := changed;
end;
 
procedure Simulate(var Grid: TGrid);
var
changed: Boolean;
begin
while Iterate(Grid) do
;
end;
 
procedure Zeros(var Grid: TGrid; Size: Integer);
var
i, j: Integer;
begin
SetLength(Grid, Size, Size);
for i := 0 to Size - 1 do
for j := 0 to Size - 1 do
Grid[i, j] := 0;
end;
 
procedure Println(Grid: TGrid);
var
i, j: Integer;
begin
for i := 0 to High(Grid) do
begin
Writeln;
for j := 0 to High(Grid[0]) do
Write(Format('%3d', [Grid[i, j]]));
end;
Writeln;
end;
 
function Grid2Bmp(Grid: TGrid): TBitmap;
const
Colors: array[0..2] of TColor = (clRed, clLime, clBlue);
var
Alength: Integer;
i: Integer;
j: Integer;
begin
Alength := Length(Grid);
 
Result := TBitmap.Create;
Result.SetSize(Alength, Alength);
 
for i := 0 to Alength - 1 do
for j := 0 to Alength - 1 do
begin
Result.Canvas.Pixels[i, j] := Colors[Grid[i, j]];
end;
end;
 
procedure Grid2P6(Grid: TGrid; FileName: TFileName);
var
f: text;
i, j, Alength: Integer;
ppm: TFileStream;
Header: AnsiString;
const
COLORS: array[0..3] of array[0..2] of byte =
// R, G, B
((0 , 0, 0),
(255 , 0, 0),
(0 , 255, 0),
(0 , 0, 255));
begin
Alength := Length(Grid);
ppm := TFileStream.Create(FileName, fmCreate);
Header := Format('P6'#10'%d %d'#10'255'#10, [Alength, Alength]);
writeln(Header);
ppm.Write(Tbytes(Header), Length(Header));
 
for i := 0 to Alength - 1 do
for j := 0 to Alength - 1 do
begin
ppm.Write(COLORS[Grid[i, j]], 3);
end;
ppm.Free;
end;
 
const
DIMENSION = 10;
 
var
Grid: TGrid;
bmp: TBitmap;
 
begin
Zeros(Grid, DIMENSION);
Grid[4, 4] := 64;
Writeln('Before:');
Println(Grid);
 
Simulate(Grid);
 
Writeln(#10'After:');
Println(Grid);
 
// Output bmp
with Grid2Bmp(Grid) do
begin
SaveToFile('output.bmp');
free;
end;
 
// Output ppm
Grid2P6(Grid, 'output.ppm');
 
Readln;
end.
 


Forth[edit]

Works with: gforth version 0.7.3


#! /usr/bin/gforth -d 20M
\ Abelian Sandpile Model
 
0 assert-level !
 
\ command-line
 
: parse-number s>number? invert throw drop ;
: parse-size ." size  : " next-arg parse-number dup . cr ;
: parse-height ." height: " next-arg parse-number dup . cr ;
: parse-args cr parse-size parse-height ;
 
parse-args constant HEIGHT constant SIZE
 
: allot-erase create here >r dup allot r> swap erase ;
: size^2 SIZE dup * cells ;
: 2cells [ 2 cells ] literal ;
: -2cells [ 2cells negate ] literal ;
 
size^2 allot-erase arr
 
\ array processing
: ix swap SIZE * + cells arr + ;
: center SIZE 2/ dup ;
: write-cell ix @ u. ;
: write-row SIZE 0 ?do dup i write-cell loop drop cr ;
: arr. SIZE 0 ?do i write-row loop ;
 
\ stack processing
 
: stack-empty? dup -1 = ;
: stack-full? stack-empty? invert ;
 
\ pgm-handling
 
: concat { a1 l1 a2 l2 } l1 l2 + allocate throw dup dup a1 swap l1 cmove a2 swap l1 + l2 cmove l1 l2 + ;
: write-pgm ." P2" cr SIZE u. SIZE u. cr ." 3" cr arr. ;
: u>s 0 <# #s #> ;
: filename s" sandpile-" SIZE u>s concat s" -" concat HEIGHT u>s concat s" .pgm" concat ;
: to-pgm filename w/o create-file throw ['] write-pgm over outfile-execute close-file throw ;
 
\ sandpile
 
: prep-arr HEIGHT center ix ! ;
: prep-stack -1 HEIGHT 4 u>= if center then ;
: prepare prep-arr prep-stack ;
: ensure if else 2drop 0 2rdrop exit then ;
: col>=0 dup 0>= ensure ;
: col<SIZE dup SIZE < ensure ;
: row>=0 over 0>= ensure ;
: row<SIZE over SIZE < ensure ;
: legal? col>=0 col<SIZE row>=0 row<SIZE 2drop true ;
: north 1. d- ;
: east 1+ ;
: south 1. d+ ;
: west 1- ;
: reduce 2dup ix dup -4 swap +! @ 4 < if 2drop then ;
: increase 2dup legal? if 2dup ix dup 1 swap +! @ 4 = if 2swap else 2drop then else 2drop then ;
: inc-north 2dup north increase ;
: inc-east 2dup east increase ;
: inc-south 2dup south increase ;
: inc-west 2dup west increase ;
: inc-all inc-north inc-east inc-south inc-west 2drop ;
: simulate prepare begin stack-full? while 2dup 2>r reduce 2r> inc-all repeat drop to-pgm ." written to " filename type cr ;
 
simulate bye
Output:

sandpile with 5000 grains of sand: ./sandpile.fs 61 5000: [1]
sandpile with 50000 grains of sand: ./sandpile.fs 201 50000: [2]
sandpile with 500000 grains of sand: ./sandpile.fs 601 500000: [3]

Fortran[edit]

Works with: gfortran version 9.2.0

The Abelian sandpile operations are defined here.

module abelian_sandpile_m
 
implicit none
 
private
public :: pile
 
type :: pile
!! usage:
!! 1) init
!! 2) run
 
integer, allocatable :: grid(:,:)
integer :: n(2)
 
contains
procedure :: init
procedure :: run
 
procedure, private :: process_node
procedure, private :: inside
end type
 
contains
 
logical function inside(this, i)
class(pile), intent(in) :: this
integer, intent(in) :: i(2)
 
inside = ((i(1) > 0) .and. (i(1) <= this%n(1)) .and. (i(2) > 0) .and. (i(2) <= this%n(2)) )
end function
 
recursive subroutine process_node(this, i)
!! start process
 
class(pile), intent(inout) :: this
integer, intent(in) :: i(2)
!! node coordinates to process
 
integer :: i0(2,2), j(2), d, k
 
! if node has more than 4 grains -> redistribute
if (this%grid(i(1),i(2)) >= 4) then
! unit vectors: help shift only one dimension (see below)
i0 = reshape([1,0,0,1], [2,2])
 
! subtract 4 grains
this%grid(i(1),i(2)) = this%grid(i(1),i(2))-4
 
! add one grain to neighbor if not out of bound
do d = 1, 2 ! loop dimensions
do k = -1, 1, 2 ! loop +-1 step in direction d
j = i+k*i0(:,d) ! j = i, but one element is shifted by +-1
if (this%inside(j)) this%grid(j(1),j(2)) = this%grid(j(1),j(2)) + 1
end do
end do
 
! check neighbor nodes
do d = 1, 2 ! loop dimensions
do k = -1, 1, 2 ! loop +-1 step in direction d
j = i+k*i0(:,d) ! j = i, but one element is shifted by +-1
if (this%inside(j)) call this%process_node(j)
end do
end do
 
! check itself
call this%process_node(i)
end if
end subroutine
 
subroutine run(this)
!! start process
 
class(pile), intent(inout) :: this
 
! only node that could be unstable is inital node
call this%process_node(this%n/2)
end subroutine
 
subroutine init(this, nx, ny, h)
class(pile), intent(out) :: this
integer, intent(in) :: nx, ny
!! grid dimensions
integer, intent(in) :: h
!! height of and grains in middle of grid
 
this%n = [nx, ny]
allocate (this%grid(nx,ny), source=0)
this%grid(nx/2, ny/2) = h
end subroutine
 
end module

The main program calls the abelian_sandpile_m and creates an ppm bitmap file by loading rgbimage_m module, which is defined here.

program main
 
use rgbimage_m
use abelian_sandpile_m
 
implicit none
 
integer :: nx, ny, i, j
 
integer :: colors(0:3,3)
 
type(rgbimage) :: im
type(pile) :: p
 
colors(0,:) = [255,255,255]
colors(1,:) = [0,0,90]
colors(2,:) = [0,0,170]
colors(3,:) = [0,0,255]
 
nx = 200
ny = 100
 
call p%init(nx, ny, 2000)
call p%run
 
call im%init(nx, ny)
 
do i = 1, nx
do j = 1, ny
call im%set_pixel(i, j, colors(p%grid(i,j),:))
end do
end do
 
call im%write('fig.ppm')
 
end program

Fōrmulæ[edit]

In this page you can see the solution of this task.

Fōrmulæ programs are not textual, visualization/edition of programs is done showing/manipulating structures but not text (more info). Moreover, there can be multiple visual representations of the same program. Even though it is possible to have textual representation —i.e. XML, JSON— they are intended for transportation effects more than visualization and edition.

The option to show Fōrmulæ programs and their results is showing images. Unfortunately images cannot be uploaded in Rosetta Code.

F#[edit]

 
// Abelian sandpile model. Nigel Galloway: July 20th., 2020
type Sandpile(x,y,N:int[])=
member private this.x=x
member private this.y=y
member private this.i=let rec topple n=match Array.tryFindIndex(fun n->n>3)n with
None->n
|Some g->let i=n.[g]/4
n.[g]<-n.[g]%4
match g%x,g/x with
(0,0)->n.[x]<-n.[x]+i;n.[1]<-n.[1]+i;topple n
|(α,0) when α=x-1->n.[g+x]<-n.[g+x]+i;n.[g-1]<-n.[g-1]+i;topple n
|(_,0)->n.[g-1]<-n.[g-1]+i;n.[g+1]<-n.[g+1]+i;n.[g+x]<-n.[g+x]+i;topple n
|(0) when β=y-1->n.[g-x]<-n.[g-x]+i;n.[g+1]<-n.[g+1]+i;topple n
|(0)->n.[g-x]<-n.[g-x]+i;n.[g+1]<-n.[g+1]+i;n.[g+x]<-n.[g+x]+i;topple n
|(α,β) when α=x-1 && β=y-1->n.[g-1]<-n.[g-1]+i;n.[g-x]<-n.[g-x]+i;topple n
|(α,_) when α=x-1->n.[g-1]<-n.[g-1]+i;n.[g-x]<-n.[g-x]+i;n.[g+x]<-n.[g+x]+i;topple n
|(_,β) when β=y-1->n.[g-1]<-n.[g-1]+i;n.[g-x]<-n.[g-x]+i;n.[g+1]<-n.[g+1]+i;topple n
|_->n.[g-1]<-n.[g-1]+i;n.[g-x]<-n.[g-x]+i;n.[g+x]<-n.[g+x]+i;n.[g+1]<-n.[g+1]+i;topple n
topple N
static member (+) (n:Sandpile, g:Sandpile)=Sandpile(n.x,n.y,Array.map2(fun n g->n+g) n.i g.i)
member this.toS=sprintf "%A" (this.i|>Array.chunkBySize x|>array2D)
 
printfn "%s\n" (Sandpile(3,3,[|4;3;3;3;1;2;0;2;3|])).toS
let e1=Array.zeroCreate<int> 25 in e1.[12]<-4; printfn "%s\n" (Sandpile(5,5,e1)).toS
let e1=Array.zeroCreate<int> 25 in e1.[12]<-6; printfn "%s\n" (Sandpile(5,5,e1)).toS
let e1=Array.zeroCreate<int> 25 in e1.[12]<-16; printfn "%s\n" (Sandpile(5,5,e1)).toS
 
Output:
[[2; 1; 0]
 [0; 3; 3]
 [1; 2; 3]]

[[0; 0; 0; 0; 0]
 [0; 0; 1; 0; 0]
 [0; 1; 0; 1; 0]
 [0; 0; 1; 0; 0]
 [0; 0; 0; 0; 0]]

[[0; 0; 0; 0; 0]
 [0; 0; 1; 0; 0]
 [0; 1; 2; 1; 0]
 [0; 0; 1; 0; 0]
 [0; 0; 0; 0; 0]]

[[0; 0; 1; 0; 0]
 [0; 2; 1; 2; 0]
 [1; 1; 0; 1; 1]
 [0; 2; 1; 2; 0]
 [0; 0; 1; 0; 0]]

Go[edit]

Translation of: Rust


Stack management in Go is automatic, starting very small (2KB) for each goroutine and expanding as necessary until the maximum allowed size is reached.

package main
 
import (
"fmt"
"log"
"os"
"strings"
)
 
const dim = 16 // image size
 
func check(err error) {
if err != nil {
log.Fatal(err)
}
}
 
// Outputs the result to the terminal using UTF-8 block characters.
func drawPile(pile [][]uint) {
chars:= []rune(" ░▓█")
for _, row := range pile {
line := make([]rune, len(row))
for i, elem := range row {
if elem > 3 { // only possible when algorithm not yet completed.
elem = 3
}
line[i] = chars[elem]
}
fmt.Println(string(line))
}
}
 
// Creates a .ppm file in the current directory, which contains
// a colored image of the pile.
func writePile(pile [][]uint) {
file, err := os.Create("output.ppm")
check(err)
defer file.Close()
// Write the signature, image dimensions and maximum color value to the file.
fmt.Fprintf(file, "P3\n%d %d\n255\n", dim, dim)
bcolors := []string{"125 0 25 ", "125 80 0 ", "186 118 0 ", "224 142 0 "}
var line strings.Builder
for _, row := range pile {
for _, elem := range row {
line.WriteString(bcolors[elem])
}
file.WriteString(line.String() + "\n")
line.Reset()
}
}
 
// Main part of the algorithm, a simple, recursive implementation of the model.
func handlePile(x, y uint, pile [][]uint) {
if pile[y][x] >= 4 {
pile[y][x] -= 4
// Check each neighbor, whether they have enough "sand" to collapse and if they do,
// recursively call handlePile on them.
if y > 0 {
pile[y-1][x]++
if pile[y-1][x] >= 4 {
handlePile(x, y-1, pile)
}
}
if x > 0 {
pile[y][x-1]++
if pile[y][x-1] >= 4 {
handlePile(x-1, y, pile)
}
}
if y < dim-1 {
pile[y+1][x]++
if pile[y+1][x] >= 4 {
handlePile(x, y+1, pile)
}
}
if x < dim-1 {
pile[y][x+1]++
if pile[y][x+1] >= 4 {
handlePile(x+1, y, pile)
}
}
 
// Uncomment this line to show every iteration of the program.
// Not recommended with large input values.
// drawPile(pile)
 
// Finally call the function on the current cell again,
// in case it had more than 4 particles.
handlePile(x, y, pile)
}
}
 
func main() {
// Create 2D grid and set size using the 'dim' constant.
pile := make([][]uint, dim)
for i := 0; i < dim; i++ {
pile[i] = make([]uint, dim)
}
 
// Place some sand particles in the center of the grid and start the algorithm.
hdim := uint(dim/2 - 1)
pile[hdim][hdim] = 16
handlePile(hdim, hdim, pile)
drawPile(pile)
 
// Uncomment this to save the final image to a file
// after the recursive algorithm has ended.
// writePile(pile)
}
Output:
                
                
                
                
                
       ░        
      ▓░▓       
     ░░ ░░      
      ▓░▓       
       ░        
                
                
                
                
                
                
       

Haskell[edit]

Works with: GHC version 8.8.1
Library: base version 4.13.0.0
Library: array version 0.5.4.0
Library: mtl version 2.2.2


Using a custom monad to make the code cleaner.

{-# LANGUAGE FlexibleContexts           #-}
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
{-# LANGUAGE ScopedTypeVariables #-}
 
module Rosetta.AbelianSandpileModel.ST
( simulate
, test
, toPGM
) where
 
import Control.Monad.Reader (asks, MonadReader (..), ReaderT, runReaderT)
import Control.Monad.ST (runST, ST)
import Control.Monad.State (evalStateT, forM_, lift, MonadState (..), StateT, modify, when)
import Data.Array.ST (freeze, readArray, STUArray, thaw, writeArray)
import Data.Array.Unboxed (array, assocs, bounds, UArray, (!))
import Data.Word (Word32)
import System.IO (hPutStr, hPutStrLn, IOMode (WriteMode), withFile)
import Text.Printf (printf)
 
type Point = (Int, Int)
type ArrayST s = STUArray s Point Word32
type ArrayU = UArray Point Word32
 
newtype M s a = M (ReaderT (S s) (StateT [Point] (ST s)) a)
deriving (Functor, Applicative, Monad, MonadReader (S s), MonadState [Point])
 
data S s = S
{ bMin :: !Point
, bMax :: !Point
, arr :: !(ArrayST s)
}
 
runM :: M s a -> S s -> [Point]-> ST s a
runM (M m) = evalStateT . runReaderT m
 
liftST :: ST s a -> M s a
liftST = M . lift . lift
 
simulate :: ArrayU -> ArrayU
simulate a = runST $ simulateST a
 
simulateST :: forall s. ArrayU -> ST s ArrayU
simulateST a = do
let (p1, p2) = bounds a
s = [p | (p, c) <- assocs a, c >= 4]
b <- thaw a :: ST s (ArrayST s)
let st = S { bMin = p1
, bMax = p2
, arr = b
}
runM simulateM st s
 
simulateM :: forall s. M s ArrayU
simulateM = do
ps <- get
case ps of
[] -> asks arr >>= liftST . freeze
p : ps' -> do
c <- changeArr p $ \x -> x - 4
when (c < 4) $ put ps'

forM_ [north, east, south, west] $ inc . ($ p)
simulateM
 
changeArr :: Point -> (Word32 -> Word32) -> M s Word32
changeArr p f = do
a <- asks arr
oldC <- liftST $ readArray a p
let newC = f oldC
liftST $ writeArray a p newC
return newC
 
inc :: Point -> M s ()
inc p = do
b <- inBounds p
when b $ do
c <- changeArr p succ
when (c == 4) $ modify $ (p :)
 
inBounds :: Point -> M s Bool
inBounds p = do
st <- ask
return $ p >= bMin st && p <= bMax st
 
north, east, south, west :: Point -> Point
north (x, y) = (x, y + 1)
east (x, y) = (x + 1, y)
south (x, y) = (x, y - 1)
west (x, y) = (x - 1, y)
 
toPGM :: ArrayU -> FilePath -> IO ()
toPGM a fp = withFile fp WriteMode $ \h -> do
let ((x1, y1), (x2, y2)) = bounds a
width = x2 - x1 + 1
height = y2 - y1 + 1
hPutStrLn h "P2"
hPutStrLn h $ show width ++ " " ++ show height
hPutStrLn h "3"
forM_ [y1 .. y2] $ \y -> do
forM_ [x1 .. x2] $ \x -> do
let c = min 3 $ a ! (x, y)
hPutStr h $ show c ++ " "
hPutStrLn h ""
 
initArray :: Int -> Word32 -> ArrayU
initArray size height = array
((-size, -size), (size, size))
[((x, y), if x == 0 && y == 0 then height else 0) | x <- [-size .. size], y <- [-size .. size]]
 
test :: Int -> Word32 -> IO ()
test size height = do
printf "size = %d, height = %d\n" size height
let a = initArray size height
b = simulate a
fp = printf "sandpile_%d_%d.pgm" size height
toPGM b fp
putStrLn $ "wrote image to " ++ fp
Output:

sandpile with 1000 grains of sand: test 15 1000: [4]
sandpile with 10000 grains of sand: test 40 10000: [5]
sandpile with 100000 grains of sand: test 150 100000: [6]
sandpile with 1000000 grains of sand: test 400 1000000: [7]

J[edit]

grid=: 4 : 'x (<<.-:2$y)} (2$y)$0'         NB. y by y grid with x grains in middle
ab=: - [: +/@(-"2 ((,-)=/~i.2)|.!.0]) 3&< NB. abelian sand pile for grid graph
require 'viewmat' NB. viewmat utility
viewmat ab ^: _ (1024 grid 25) NB. visual

Java[edit]

This is based on the JavaScript implementation linked to in the task description.

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
 
public class AbelianSandpile {
public static void main(String[] args) {
SwingUtilities.invokeLater(new Runnable() {
public void run() {
Frame frame = new Frame();
frame.setVisible(true);
}
});
}
 
private static class Frame extends JFrame {
private Frame() {
super("Abelian Sandpile Model");
setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
Container contentPane = getContentPane();
JPanel controlPanel = new JPanel(new FlowLayout(FlowLayout.LEFT));
JButton start = new JButton("Restart Simulation");
start.addActionListener(e -> restartSimulation());
JButton stop = new JButton("Stop Simulation");
stop.addActionListener(e -> stopSimulation());
controlPanel.add(start);
controlPanel.add(stop);
contentPane.add(controlPanel, BorderLayout.NORTH);
contentPane.add(canvas = new Canvas(), BorderLayout.CENTER);
timer = new Timer(100, e -> canvas.runAndDraw());
timer.start();
pack();
}
 
private void restartSimulation() {
timer.stop();
canvas.initGrid();
timer.start();
}
 
private void stopSimulation() {
timer.stop();
}
 
private Timer timer;
private Canvas canvas;
}
 
private static class Canvas extends JComponent {
private Canvas() {
setBorder(BorderFactory.createEtchedBorder());
setPreferredSize(new Dimension(600, 600));
}
 
public void paintComponent(Graphics g) {
int width = getWidth();
int height = getHeight();
g.setColor(Color.WHITE);
g.fillRect(0, 0, width, height);
int cellWidth = width/GRID_LENGTH;
int cellHeight = height/GRID_LENGTH;
for (int i = 0; i < GRID_LENGTH; ++i) {
for (int j = 0; j < GRID_LENGTH; ++j) {
if (grid[i][j] > 0) {
g.setColor(COLORS[grid[i][j]]);
g.fillRect(i * cellWidth, j * cellHeight, cellWidth, cellHeight);
}
}
}
}
 
private void initGrid() {
for (int i = 0; i < GRID_LENGTH; ++i) {
for (int j = 0; j < GRID_LENGTH; ++j) {
grid[i][j] = 0;
}
}
}
 
private void runAndDraw() {
for (int i = 0; i < 100; ++i)
addSand(GRID_LENGTH/2, GRID_LENGTH/2);
repaint();
}
 
private void addSand(int i, int j) {
int grains = grid[i][j];
if (grains < 3) {
grid[i][j]++;
}
else {
grid[i][j] = grains - 3;
if (i > 0)
addSand(i - 1, j);
if (i < GRID_LENGTH - 1)
addSand(i + 1, j);
if (j > 0)
addSand(i, j - 1);
if (j < GRID_LENGTH - 1)
addSand(i, j + 1);
}
}
 
private int[][] grid = new int[GRID_LENGTH][GRID_LENGTH];
}
 
private static final Color[] COLORS = {
Color.WHITE,
new Color(0x00, 0xbf, 0xff),
new Color(0xff, 0xd7, 0x00),
new Color(0xb0, 0x30, 0x60)
};
private static final int GRID_LENGTH = 300;
}
Output:

See: abelian_sandpile.png (offsite PNG image)

Julia[edit]

Modified from code by Hayk Aleksanyan, viewable at github.com/hayk314/Sandpiles, license viewable there.

module AbelSand
 
# supports output functionality for the results of the sandpile simulations
# outputs the final grid in CSV format, as well as an image file
 
using CSV, DataFrames, Images
 
function TrimZeros(A)
# given an array A trims any zero rows/columns from its borders
# returns a 4 tuple of integers, i1, i2, j1, j2, where the trimmed array corresponds to A[i1:i2, j1:j2]
# A can be either numeric or a boolean array
 
i1, j1 = 1, 1
i2, j2 = size(A)
 
zz = typeof(A[1, 1])(0) # comparison of a value takes into account the type as well
 
# i1 is the first row which has non zero element
for i = 1:size(A, 1)
q = false
for k = 1:size(A, 2)
if A[i, k] != zz
q = true
i1 = i
break
end
end
 
if q == true
break
end
end
 
# i2 is the first from below row with non zero element
for i in size(A, 1):-1:1
q = false
for k = 1:size(A, 2)
if A[i, k] != zz
q = true
i2 = i
break
end
end
 
if q == true
break
end
end
 
# j1 is the first column with non zero element
 
for j = 1:size(A, 2)
q = false
for k = 1:size(A, 1)
if A[k, j] != zz
j1 = j
q = true
break
end
end
 
if q == true
break
end
end
 
# j2 is the last column with non zero element
 
for j in size(A, 2):-1:1
q=false
for k=1:size(A,1)
if A[k, j] != zz
j2 = j
q=true
break
end
end
 
if q==true
break
end
end
 
return i1, i2, j1, j2
end
 
function addLayerofZeros(A, extraLayer)
# adds layer of zeros from all corners to the given array A
 
if extraLayer <= 0
return A
end
 
N, M = size(A)
 
 
Z = zeros( typeof(A[1,1]), N + 2*extraLayer, M + 2*extraLayer)
Z[(extraLayer+1):(N + extraLayer ), (extraLayer+1):(M+extraLayer)] = A
 
return Z
 
end
 
function printIntoFile(A, extraLayer, strFileName, TrimSmallValues = false)
# exports a 2d matrix A into a csv file
# @extraLayer is an integers adding layer of 0-s sorrounding the output matrix
 
# trimming off very small values; tiny values affect the performance of CSV export
if TrimSmallValues == true
A = map(x -> if (abs(x - floor(x)) < 0.01) floor(x) else x end, A)
end
 
i1, i2, j1, j2 = TrimZeros( A )
A = A[i1:i2, j1:j2]
 
A = addLayerofZeros(A, extraLayer)
 
CSV.write(string(strFileName,".csv"), DataFrame(A), writeheader = false)
 
return A
 
end
 
function Array_magnifier(A, cell_mag, border_mag)
# A is the main array; @cell_mag is the magnifying size of the cell,
# @border_mag is the magnifying size of the border between lattice cells
 
# creates a new array where each cell of the original array A appears magnified by size = cell_mag
 
 
total_factor = cell_mag + border_mag
 
A1 = zeros(typeof(A[1, 1]), total_factor*size(A, 1), total_factor*size(A, 2))
 
for i = 1:size(A,1), j = 1:size(A,2), u = ((i-1)*total_factor+1):(i*total_factor),
v = ((j-1)*total_factor+1):(j*total_factor)
if(( u - (i - 1) * total_factor <= cell_mag) && (v - (j - 1) * total_factor <= cell_mag))
A1[u, v] = A[i, j]
end
end
 
return A1
 
end
 
function saveAsGrayImage(A, fileName, cell_mag, border_mag, TrimSmallValues = false)
# given a 2d matrix A, we save it as a gray image after magnifying by the given factors
A1 = Array_magnifier(A, cell_mag, border_mag)
A1 = A1/maximum(maximum(A1))
 
# trimming very small values from A1 to improve performance
if TrimSmallValues == true
A1 = map(x -> if ( x < 0.01) 0.0 else round(x, digits = 2) end, A1)
end
 
save(string(fileName, ".png") , colorview(Gray, A1))
end
 
function saveAsRGBImage(A, fileName, color_codes, cell_mag, border_mag)
# color_codes is a dictionary, where key is a value in A and value is an RGB triplet
# given a 2d array A, and color codes (mapping from values in A to RGB triples), save A
# into fileName as png image after applying the magnifying factors
 
A1 = Array_magnifier(A, cell_mag, border_mag)
color_mat = zeros(UInt8, (3, size(A1, 1), size(A1, 2)))
 
for i = 1:size(A1,1)
for j = 1:size(A1,2)
color_mat[:, i, j] = get(color_codes, A1[i, j] , [0, 0, 0])
end
end
 
save(string(fileName, ".png") , colorview(RGB, color_mat/255))
end
 
const N_size = 700 # the radius of the lattice Z^2, the actual size becomes (2*N+1)x(2*N+1)
const dx = [1, 0, -1, 0] # for a given (x,y) in Z^2, (x + dx, y + dy) for all (dx,dy) covers the neighborhood of (x,y)
const dy = [0, 1, 0, -1]
 
struct L_coord
# represents a lattice coordinate
x::Int
y::Int
end
 
function FindCoordinate(Z::Array{L_coord,1}, a::Int, b::Int)
# in the given array Z of coordinates finds the (first) index of the tuple (a,b)
# if no match, returns -1
 
for i=1:length(Z)
if (Z[i].x == a) && (Z[i].y == b)
return i
end
end
 
return -1
end
 
function move(N)
# the main function moving the pile sand grains of size N at the origin of Z^2 until the sandpile becomes stable
 
Z_lat = zeros(UInt8, 2 * N_size + 1, 2 * N_size + 1) # models the integer lattice Z^2, we will have at most 4 sands on each vertex
V_sites = falses(2 * N_size + 1, 2 * N_size + 1) # all sites which are visited by the sandpile process, are being marked here
Odometer = zeros(UInt64, 2 * N_size + 1, 2 * N_size + 1) # stores the values of the odometer function
 
 
walking = L_coord[] # the coordinates of sites which need to move
 
V_sites[N_size + 1, N_size + 1] = true
 
# i1, ... j2 -> show the boundaries of the box which is visited by the sandpile process
i1, i2, j1, j2 = N_size + 1, N_size + 1, N_size + 1, N_size + 1
n = N
 
t1 = time_ns()
 
while n > 0
n -= 1
 
Z_lat[N_size + 1, N_size + 1] += 1
if (Z_lat[N_size + 1, N_size + 1] >= 4)
push!(walking, L_coord(N_size + 1, N_size + 1))
end
 
while(length(walking) > 0)
w = pop!(walking)
x = w.x
y = w.y
 
Z_lat[x, y] -= 4
Odometer[x, y] += 4
 
for k = 1:4
Z_lat[x + dx[k], y + dy[k]] += 1
V_sites[x + dx[k], y + dy[k]] = true
if Z_lat[x + dx[k], y + dy[k]] >= 4
if FindCoordinate(walking, x + dx[k] , y + dy[k]) == -1
push!(walking, L_coord( x + dx[k], y + dy[k]))
end
end
end
 
i1 = min(i1, x - 1)
i2 = max(i2, x + 1)
j1 = min(j1, y - 1)
j2 = max(j2, y + 1)
end
 
 
end #end of the main while
t2 = time_ns()
 
println("The final boundaries are:: ", (i2 - i1 + 1),"x",(j2 - j1 + 1), "\n")
print("time elapsed: " , (t2 - t1) / 1.0e9, "\n")
 
Z_lat = printIntoFile(Z_lat, 0, string("Abel_Z_", N))
Odometer = printIntoFile(Odometer, 1, string("Abel_OD_", N))
 
saveAsGrayImage(Z_lat, string("Abel_Z_", N), 20, 0)
color_code = Dict(1=>[255, 128, 255], 2=>[255, 0, 0],3 => [0, 128, 255])
saveAsRGBImage(Z_lat, string("Abel_Z_color_", N), color_code, 20, 0)
 
# for the total elapsed time, it's better to use the @time macros on the main call
 
return Z_lat, Odometer # these are trimmed in output module
 
end # end of function move
 
 
end # module
 
 
using .AbelSand
 
Z_lat, Odometer = AbelSand.move(100000)
 
Output:

Link to PNG output file for N=100000 ie. AbelSand.move(100000)
Link to PNG output file (run time >90 min) for N=1000000 (move(1000000))

Nim[edit]

Library: nimPNG

Our program uses Rust algorithm (and also its colors 🙂) and the formula to compute grid size from number of particles comes from Pascal algorithm. Number of particles is an input from user. The program displays the values on the terminal if there are not too many and produce a PNG image. Code to produce a PPM image is also provided but not used.

 
# Abelian sandpile.
 
from math import sqrt
from nimPNG import savePNG24
from sequtils import repeat
from strformat import fmt
from strutils import strip, addSep, parseInt
 
# The grid represented as a sequence of sequences of int32.
type Grid = seq[seq[int32]]
 
# Colors to use for PPM and PNG files.
const Colors = [[byte 100, 40, 15],
[byte 117, 87, 30],
[byte 181, 134, 47],
[byte 245, 182, 66]]
 
#---------------------------------------------------------------------------------------------------
 
func sideLength(initVal: int32): int32 =
# Return the grid side length needed for "initVal" particles.
# We make sure that the returned value is odd.
result = sqrt(initVal.toFloat / 1.75).int32 + 3
result += result and 1 xor 1
 
#---------------------------------------------------------------------------------------------------
 
func doOneStep(grid: var Grid; boundary: var array[4, int]): bool =
## Compute one step.
 
result = false
 
for y in boundary[0]..boundary[2]:
for x in boundary[1]..boundary[3]:
if grid[y][x] >= 4:
 
let rem = grid[y][x] div 4
grid[y][x] = grid[y][x] mod 4
 
if y - 1 >= 0:
inc grid[y - 1][x], rem
if y == boundary[0]:
dec boundary[0]
 
if x - 1 >= 0:
inc grid[y][x - 1], rem
if x == boundary[1]:
dec boundary[1]
 
if y + 1 < grid.len:
inc grid[y + 1][x], rem
if y == boundary[2]:
inc boundary[2]
 
if x + 1 < grid.len:
inc grid[y][x + 1], rem
if x == boundary[3]:
inc boundary[3]
 
result = true
 
#---------------------------------------------------------------------------------------------------
 
proc display(grid: Grid; initVal: int) =
## Display the grid as an array of values.
 
echo fmt"Starting with {initVal} particles."
echo ""
 
var line = newStringOfCap(2 * grid.len - 1)
for row in grid:
for value in row:
line.addSep(" ", 0)
line.add($value)
echo line
line.setLen(0)
echo ""
 
#---------------------------------------------------------------------------------------------------
 
proc writePpmFile(grid: Grid; name: string) =
## Write a grid representation in a PPM file.
 
var file = open(name, fmWrite)
file.write(fmt"P6 {grid.len} {grid.len} 255 ")
 
for row in grid:
for value in row:
discard file.writeBytes(Colors[value], 0, 3)
 
file.close()
echo fmt"PPM image written in ""{name}""."
 
#---------------------------------------------------------------------------------------------------
 
proc writePngFile(grid: Grid; name: string) =
## Write a grid representation in a PNG file.
 
var pixels = newSeq[byte](3 * grid.len * grid.len)
 
# Build pixel list.
var idx = 0
for row in grid:
for value in row:
pixels[idx..idx+2] = Colors[value]
inc idx, 3
 
discard savePNG24(name, pixels, grid.len, grid.len)
echo fmt"PNG image written in ""{name}""."
 
#---------------------------------------------------------------------------------------------------
 
proc askInitVal(): int32 =
# Ask user for the number of particles.
 
while true:
stdout.write("Number of particles? ")
try:
let input = stdin.readLine().strip().parseInt()
if input in 4..int32.high:
return input.int32
echo fmt"Value not in expected range: 4..{int32.high}"
except ValueError:
echo "Invalid input"
except EOFError:
quit(QuitSuccess)
 
#---------------------------------------------------------------------------------------------------
 
# Initialize the grid.
let initVal = askInitVal()
let sideLen = sideLength(initVal)
var grid = repeat(newSeq[int32](sideLen), sideLen)
let origin = grid.len div 2
var boundaries: array[4, int] = [origin, origin, origin, origin]
grid[origin][origin] = initVal
 
# Run the simulation.
while doOneStep(grid, boundaries):
discard
 
# Display grid.
if grid.len <= 20:
grid.display(initVal)
#grid.writePpmFile(fmt"grid_{initVal}.ppm")
grid.writePngFile(fmt"grid_{initVal}.png")
 
Output:
Number of particles? 100
Starting with 100 particles.

0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 1 2 1 0 0 0 0
0 0 0 3 2 0 2 3 0 0 0
0 0 3 0 3 2 3 0 3 0 0
0 1 2 3 0 3 0 3 2 1 0
0 2 0 2 3 0 3 2 0 2 0
0 1 2 3 0 3 0 3 2 1 0
0 0 3 0 3 2 3 0 3 0 0
0 0 0 3 2 0 2 3 0 0 0
0 0 0 0 1 2 1 0 0 0 0
0 0 0 0 0 0 0 0 0 0 0

PNG image written in "grid_100.png".

Pascal[edit]

Works with: Free Pascal
The main optimization was to spread the sand immediatly.
mul := val DIV 4;//not only := val -4 
so that only (sand mod 4) stays in place.runtime for abelian(1e6) down to 1min 20 secs from 9 min

Memorizing the used colums of the rows has little effect when choosing the right size of the grid.Only 11 secs for abelian(1e6) -> 1min 9sec
Python shows 64 too.

 
program Abelian2;
{$IFDEF FPC}
{$MODE DELPHI}{$OPTIMIZATION ON,ALL}{$CODEALIGN proc=16}{$ALIGN 16}
{$ELSE}
{$APPTYPE CONSOLE}
{$ENDIF}
uses
SysUtils;
 
type
Tlimit = record
lmtLow,LmtHigh : LongWord;
end;
TRowlimits = array of Tlimit;
tOneRow = pLongWord;
tGrid = array of LongWord;
 
var
Grid: tGrid;
Rowlimits:TRowlimits;
s : AnsiString;
maxval,maxCoor : NativeUint;
 
function CalcMaxCoor(maxVal : NativeUint):NativeUint;
// maxVal = 10000;maxCoor = 77-2;// maxCoor*maxCoor *1,778; 0.009sec
// maxVal = 100000;maxCoor = 236-2;// maxCoor*maxCoor *1.826; 0.825sec
// maxVal = 1000000;maxCoor = 732-2;// maxCoor*maxCoor *1.877; 74 sec
Begin
result := trunc(sqrt(maxval/1.75))+3;
end;
 
procedure clear;
begin
setlength(Grid,0);
setlength(Rowlimits,0);
s := '';
end;
 
procedure InitGrid(var G:tGrid;InitVal:NativeUint);
var
row,middle: nativeINt;
begin
// setlength(Rowlimits,0); setlength(G,0);
MaxCoor := CalcMaxCoor(InitVal);
setlength(G,sqr(maxCoor));
setlength(Rowlimits,maxCoor);
fillchar(G[0],length(G)*SizeOf(G[0]),#0);
 
middle := (maxCoor) div 2;
Grid[middle*maxcoor+middle] := InitVal;
For row := 1 to maxCoor do
with Rowlimits[row] do
Begin
lmtLow := middle;
lmtHigh := middle;
end;
 
with Rowlimits[middle] do
Begin
lmtLow := middle;
lmtHigh := middle;
end;
end;
procedure OutGridPPM(const G:tGrid;maxValue : NativeUint);
const
color : array[0..3] of array[0..2] of Byte =
//R,G,B)
((0,0,0),
(255,0,0),
(0,255,0),
(0,0,255));
var
f :text;
pActRow: tOneRow;
col,row,sIdx,value : NativeInt;
Begin
Assignfile(f,'ppm/Grid_'+IntToStr(maxValue)+'.ppm');
rewrite(f);
write(f,Format('P6 %d %d %d ',[maxCoor-1,maxCoor-1,255]));
setlength(s,(maxCoor-1)*3);
pActRow :=@G[0];
For row := maxCoor-2 downto 0 do
Begin
inc(pActRow,maxCoor);
sIdx := 1;
For col := 1 to maxCoor-1 do
Begin
value := pActRow[col];
s[sIdx] := CHR(color[value,0]);
s[sIdx+1] := CHR(color[value,1]);
s[sIdx+2] := CHR(color[value,2]);
inc(sIdx,3);
end;
write(f,s);
end;
CloseFile(f);
end;
 
procedure OutGrid(const G:tGrid);
//output of grid and test, if no sand is lost
var
pActRow: tOneRow;
col,row,sum,value : NativeUint;
Begin
setlength(s,maxcoor-1);
pActRow := @G[0];
sum := 0;
For row := maxCoor-1 downto 1 do
Begin
inc(pActRow,maxcoor);
For col := 1 to maxCoor-1 do
Begin
value := pActRow[col];
// IF value>=4 then writeln(row:5,col:5,value:13);
s[col] := chr(value+48);
inc(sum,value);
end;
if maxCoor <80 then
writeln(s);
end;
writeln('columns ',maxcoor-1,' checksum ',maxVal,' ?=? ',sum);
{
For row := 1 to maxCoor do
with Rowlimits[row] do
writeln(lmtLow:10,lmtHigh:10);
* }

end;
 
procedure Evolution(var G:tGrid);
var
pActRow,pRowBefore,pRowAfter : tOneRow;
col,row,mul,val,done : NativeUint;
begin
repeat
pRowBefore := @G[0];
pActRow := @G[maxcoor];
pRowAfter := @G[2*maxcoor];
done := 0;
For row := maxCoor-1 downto 1 do
Begin
with RowLimits[row] do
Begin
while (LmtLow >1) AND (pActRow[lmtLow]<> 0) do
dec(lmtLow);
while (lmtHigh < maxCoor) AND (pActRow[lmtHigh]<> 0) do
inc(lmtHigh);
For col := lmtLow to lmtHigh do
Begin
val := pActRow[col];
IF val >=4 then
Begin
mul := val DIV 4;
done := val;
inc(pRowBefore[col],mul);
inc(pActRow[col-1],mul);
pActRow[col] := val-4*Mul;
inc(pActRow[col+1],mul);
inc(pRowAfter[col],mul);
end;
end;
pRowBefore:= pActRow;
pActRow := pRowAfter;
inc(pRowAfter,maxcoor);
end;
end;
until done=0;
end;
 
procedure OneTurn(count:NativeUint);
begin
Writeln(' Test abelian sandpile( ',count,' )');
MaxVal := count;
InitGrid(Grid,count);
Evolution(Grid);
OutGrid(Grid);
OutGridPPM(Grid,count);
clear;
end;
 
BEGIN
OneTurn(4);
OneTurn(16);
OneTurn(64);
OneTurn(1000);
OneTurn(10000);
OneTurn(100000);
END.
 
Output:
 Test abelian sandpile( 4 )
010
101
010
columns 3 checksum 4 ?=? 4
 Test abelian sandpile( 16 )
00100
02120
11011
02120
00100
columns 5 checksum 16 ?=? 16
 Test abelian sandpile( 64 )
00121000
02222200
12222210
22202220
12222210
02222200
00121000
00000000
columns 8 checksum 64 ?=? 64
 Test abelian sandpile( 1000 )
0000000001111111000000000
0000000130233320310000000
0000013223313133223100000
0000213222130312223120000
0002220123332333210222000
0011223233123213323221100
0033032313221223132303300
0122123203311133023212210
0322231023333333201322230
1032333332231322333332301
1231312332232322332131321
1313322133322233312233131
1330231131220221311320331
1313322133322233312233131
1231312332232322332131321
1032333332231322333332301
0322231023333333201322230
0122123203311133023212210
0033032313221223132303300
0011223233123213323221100
0002220123332333210222000
0000213222130312223120000
0000013223313133223100000
0000000130233320310000000
0000000001111111000000000
columns 25 checksum 1000 ?=? 1000
 Test abelian sandpile( 10000 )
--shortened
columns 77 checksum 10000 ?=? 10000
 Test abelian sandpile( 100000 )
columns 241 checksum 100000 ?=? 100000

real    0m0,815s

Perl[edit]

#!/usr/bin/perl
 
use strict; # http://www.rosettacode.org/wiki/Abelian_sandpile_model
use warnings;
 
my ($high, $wide) = split ' ', qx(stty size);
my $mask = "\0" x $wide . ("\0" . "\177" x ($wide - 2) . "\0") x ($high - 5) .
"\0" x $wide;
my $pile = $mask =~ s/\177/ rand() < 0.02 ? chr 64 + rand 20 : "\0" /ger;
 
for ( 1 .. 1e6 )
{
print "\e[H", $pile =~ tr/\0-\177/ 1-~/r, "\n$_";
my $add = $pile =~ tr/\1-\177/\0\0\0\200/r; # set high bit for >=4
$add =~ /\200/ or last;
$pile =~ tr/\4-\177/\0-\173/; # subtract 4 if >=4
for ("\0$add", "\0" x $wide . $add, substr($add, 1), substr $add, $wide)
{
$pile |= $_;
$pile =~ tr/\200-\377/\1-\176/; # add one to each neighbor of >=4
$pile &= $mask;
}
select undef, undef, undef, 0.1; # comment out for full speed
}

Phix[edit]

Library: Phix/pGUI

Generates moving images similar to the julia output. The distributed version also has variable speed, additional display modes, and a random dropping toggle.

-- demo\rosetta\Abelian_sandpile_model.exw
include pGUI.e
 
Ihandle dlg, canvas
cdCanvas cddbuffer
 
sequence board = {{0,0,0},
{0,0,0},
{0,0,0}}
 
procedure drop(integer y, x)
sequence moves = {}
while true do
board[y,x] += 1
if board[y,x]>=4 then
board[y,x] -= 4
moves &= {{y,x-1},{y,x+1},{y-1,x},{y+1,x}}
end if
-- extend board if rqd (maintain a border of zeroes)
if x=1 then -- extend left
for i=1 to length(board) do
board[i] = prepend(board[i],0)
end for
for i=1 to length(moves) do
moves[i][2] += 1
end for
elsif x=length(board[1]) then -- extend right
for i=1 to length(board) do
board[i] = append(board[i],0)
end for
end if
-- (copy the all-0 lines from the other end...)
if y=1 then -- extend up
board = prepend(board,board[$])
for i=1 to length(moves) do
moves[i][1] += 1
end for
elsif y=length(board) then -- extend down
board = append(board,board[1])
end if
if length(moves)=0 then exit end if
{y,x} = moves[$]
moves = moves[1..$-1]
end while
IupUpdate(canvas)
end procedure
 
function timer_cb(Ihandle /*ih*/)
integer y = floor(length(board)/2)+1,
x = floor(length(board[1])/2)+1
drop(y,x)
return IUP_DEFAULT
end function
 
function redraw_cb(Ihandle ih, integer /*posx*/, integer /*posy*/)
IupGLMakeCurrent(ih)
cdCanvasActivate(cddbuffer)
cdCanvasClear(cddbuffer)
for y=1 to length(board) do
for x=1 to length(board[1]) do
integer c = board[y][x]
if c!=0 then
integer colour = {CD_VIOLET,CD_RED,CD_BLUE}[c]
cdCanvasPixel(cddbuffer, x, y, colour)
end if
end for
end for
cdCanvasFlush(cddbuffer)
return IUP_DEFAULT
end function
 
function map_cb(Ihandle ih)
IupGLMakeCurrent(ih)
atom res = IupGetDouble(NULL, "SCREENDPI")/25.4
cddbuffer = cdCreateCanvas(CD_GL, "300x100 %g", {res})
cdCanvasSetBackground(cddbuffer, CD_PARCHMENT)
return IUP_DEFAULT
end function
 
procedure main()
IupOpen()
canvas = IupGLCanvas("RASTERSIZE=300x100")
IupSetCallbacks({canvas}, {"ACTION", Icallback("redraw_cb"),
"MAP_CB", Icallback("map_cb")})
dlg = IupDialog(canvas,"TITLE=\"Abelian sandpile model\"")
IupCloseOnEscape(dlg)
IupShow(dlg)
Ihandle timer = IupTimer(Icallback("timer_cb"), 10)
IupMainLoop()
IupClose()
end procedure
 
main()

Python[edit]

 
import numpy as np
import matplotlib.pyplot as plt
 
 
def iterate(grid):
changed = False
for ii, arr in enumerate(grid):
for jj, val in enumerate(arr):
if val > 3:
grid[ii, jj] -= 4
if ii > 0:
grid[ii - 1, jj] += 1
if ii < len(grid)-1:
grid[ii + 1, jj] += 1
if jj > 0:
grid[ii, jj - 1] += 1
if jj < len(grid)-1:
grid[ii, jj + 1] += 1
changed = True
return grid, changed
 
 
def simulate(grid):
while True:
grid, changed = iterate(grid)
if not changed:
return grid
 
 
if __name__ == '__main__':
start_grid = np.zeros((10, 10))
start_grid[4:5, 4:5] = 64
final_grid = simulate(start_grid.copy())
plt.figure()
plt.gray()
plt.imshow(start_grid)
plt.figure()
plt.gray()
plt.imshow(final_grid)
 

Output: </n> Before:

 
[[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0.64. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]]
 

After:

 
[[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 1. 2. 1. 0. 0. 0. 0.]
[0. 0. 2. 2. 2. 2. 2. 0. 0. 0.]
[0. 1. 2. 2. 2. 2. 2. 1. 0. 0.]
[0. 2. 2. 2. 0. 2. 2. 2. 0. 0.]
[0. 1. 2. 2. 2. 2. 2. 1. 0. 0.]
[0. 0. 2. 2. 2. 2. 2. 0. 0. 0.]
[0. 0. 0. 1. 2. 1. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]
[0. 0. 0. 0. 0. 0. 0. 0. 0. 0.]]
 


An interactive variant to the above solution:

 
from os import system, name
from time import sleep
 
def clear():
if name == 'nt':
_ = system('cls')
else: _ = system('clear')
 
def exit():
import sys
clear()
sys.exit()
 
def make_area(x, y):
area = [[0]*x for _ in range(y)]
return area
 
def make_sandpile(area, loc, height):
loc=list(n-1 for n in loc)
x, y = loc
 
try: area[y][x]+=height
except IndexError: pass
 
def run(area, by_frame=False):
def run_frame():
for y_index, group in enumerate(area):
y = y_index+1
 
for x_index, height in enumerate(group):
x = x_index+1
 
if height < 4: continue
 
else:
make_sandpile(area, (x+1, y), 1)
make_sandpile(area, (x, y+1), 1)
 
if x_index-1 >= 0:
make_sandpile(area, (x-1, y), 1)
if y_index-1 >= 0:
make_sandpile(area, (x, y-1), 1)
 
make_sandpile(area, (x, y), -4)
 
while any([any([pile>=4 for pile in group]) for group in area]):
if by_frame:
clear()
run_frame()
if by_frame:
show_area(area); sleep(.05)
 
def show_area(area):
display = [' '.join([str(item) if item else ' ' for item in group])
for group in area]
[print(i) for i in display]
 
clear()
if __name__ == '__main__':
area = make_area(10, 10)
print('\nBefore:')
show_area(area)
make_sandpile(area, (5, 5), 64)
run(area)
print('\nAfter:')
show_area(area)
 

Output:

 
Before:
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
 
After:
0 0 0 0 0 0 0 0 0 0
0 0 0 1 2 1 0 0 0 0
0 0 2 2 2 2 2 0 0 0
0 1 2 2 2 2 2 1 0 0
0 2 2 2 0 2 2 2 0 0
0 1 2 2 2 2 2 1 0 0
0 0 2 2 2 2 2 0 0 0
0 0 0 1 2 1 0 0 0 0
0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0
 

Raku[edit]

(formerly Perl 6)

Terminal based[edit]

Works with: Rakudo version 2019.07.1

Defaults to a stack of 1000 and showing progress. Pass in a custom stack size if desired and -hide-progress to run without displaying progress (much faster.)

sub cleanup { print "\e[0m\e[?25h\n"; exit(0) }
 
signal(SIGINT).tap: { cleanup(); exit(0) }
 
unit sub MAIN ($stack = 1000, :$hide-progress = False );
 
my @color = "\e[38;2;0;0;0m█",
"\e[38;2;255;0;0m█",
"\e[38;2;255;255;0m█",
"\e[38;2;0;0;255m█",
"\e[38;2;255;255;255m█"
;
 
my ($h, $w) = qx/stty size/.words».Int;
my $buf = $w * $h;
my @buffer = 0 xx $buf;
my $done;
 
@buffer[$w * ($h div 2) + ($w div 2) - 1] = $stack;
 
print "\e[?25l\e[48;5;232m";
 
repeat {
$done = True;
loop (my int $row; $row < $h; $row = $row + 1) {
my int $rs = $row * $w; # row start
my int $re = $rs + $w; # row end
loop (my int $idx = $rs; $idx < $re; $idx = $idx + 1) {
if @buffer[$idx] >= 4 {
my $grains = @buffer[$idx] div 4;
@buffer[ $idx - $w ] += $grains if $row > 0;
@buffer[ $idx - 1 ] += $grains if $idx - 1 >= $rs;
@buffer[ $idx + $w ] += $grains if $row < $h - 1;
@buffer[ $idx + 1 ] += $grains if $idx + 1 < $re;
@buffer[ $idx ] %= 4;
$done = False;
}
}
}
unless $hide-progress {
print "\e[1;1H", @buffer.map( { @color[$_ min 4] }).join;
}
} until $done;
 
print "\e[1;1H", @buffer.map( { @color[$_ min 4] }).join;
 
cleanup;

Passing in 2048 as a stack size results in: Abelian-sandpile-model-perl6.png (offsite .png image)

SDL2 Animation[edit]

use NativeCall;
use SDL2::Raw;
 
my ($width, $height) = 900, 900;
 
unit sub MAIN ($stack = 10000);
 
my int ($w, $h) = 160, 160;
 
my $buf = $w * $h;
my @buffer = 0 xx $buf;
 
@buffer[$w * ($h div 2) + ($w div 2) - 1] = $stack;
 
 
SDL_Init(VIDEO);
 
my SDL_Window $window = SDL_CreateWindow(
"Abelian sandpile - Raku",
SDL_WINDOWPOS_CENTERED_MASK, SDL_WINDOWPOS_CENTERED_MASK,
$width, $height,
RESIZABLE
);
 
my SDL_Renderer $renderer = SDL_CreateRenderer( $window, -1, ACCELERATED +| TARGETTEXTURE );
 
my $asp_texture = SDL_CreateTexture($renderer, %PIXELFORMAT<RGB332>, STREAMING, $w, $h);
 
my $pixdatabuf = CArray[int64].new(0, $w, $h, $w);
 
my @color = 0x00, 0xDE, 0x14, 0xAA, 0xFF;
 
sub render {
my int $pitch;
my int $cursor;
 
# work-around to pass the pointer-pointer.
my $pixdata = nativecast(Pointer[int64], $pixdatabuf);
SDL_LockTexture($asp_texture, SDL_Rect, $pixdata, $pitch);
 
$pixdata = nativecast(CArray[int8], Pointer.new($pixdatabuf[0]));
 
loop (my int $row; $row < $h; $row = $row + 1) {
my int $rs = $row * $w; # row start
my int $re = $rs + $w; # row end
loop (my int $idx = $rs; $idx < $re; $idx = $idx + 1) {
$pixdata[$idx] = @buffer[$idx] < 4 ?? @color[@buffer[$idx]] !! @color[4];
if @buffer[$idx] >= 4 {
my $grains = floor @buffer[$idx] / 4;
@buffer[ $idx - $w ] += $grains if $row > 0;
@buffer[ $idx - 1 ] += $grains if $idx - 1 >= $rs;
@buffer[ $idx + $w ] += $grains if $row < $h - 1;
@buffer[ $idx + 1 ] += $grains if $idx + 1 < $re;
@buffer[ $idx ] %= 4;
}
}
}
 
SDL_UnlockTexture($asp_texture);
 
SDL_RenderCopy($renderer, $asp_texture, SDL_Rect, SDL_Rect.new(:x(0), :y(0), :w($width), :h($height)));
SDL_RenderPresent($renderer);
}
 
my $event = SDL_Event.new;
 
main: loop {
 
while SDL_PollEvent($event) {
my $casted_event = SDL_CastEvent($event);
 
given $casted_event {
when *.type == QUIT {
last main;
}
}
}
 
render();
print fps;
}
 
say '';
 
sub fps {
state $fps-frames = 0;
state $fps-now = now;
state $fps = '';
$fps-frames++;
if now - $fps-now >= 1 {
$fps = [~] "\b" x 40, ' ' x 20, "\b" x 20 ,
sprintf "FPS: %5.2f ", ($fps-frames / (now - $fps-now)).round(.01);
$fps-frames = 0;
$fps-now = now;
}
$fps
}

Passing in a stack size of 20000 results in: Abelian-sandpile-sdl2.png (offsite .png image)

Rust[edit]

// This is the main algorithm.
//
// It loops over the current state of the sandpile and updates it on-the-fly.
fn advance(field: &mut Vec<Vec<usize>>, boundary: &mut [usize; 4]) -> bool
{
// This variable is used to check whether we changed anything in the array. If no, the loop terminates.
let mut done = false;
 
for y in boundary[0]..boundary[2]
{
for x in boundary[1]..boundary[3]
{
if field[y][x] >= 4
{
// This part was heavily inspired by the Pascal version. We subtract 4 as many times as we can
// and distribute it to the neighbors. Also, in case we have outgrown the current boundary, we
// update it to once again contain the entire sandpile.
 
// The amount that gets added to the neighbors is the amount here divided by four and (implicitly) floored.
// The remaining sand is just current modulo 4.
let rem: usize = field[y][x] / 4;
field[y][x] %= 4;
 
// The isize casts are necessary because usize can not go below 0.
// Also, the reason why x and y are compared to boundary[2]-1 and boundary[3]-1 is because for loops in
// Rust are upper bound exclusive. This means a loop like 0..5 will only go over 0,1,2,3 and 4.
if y as isize - 1 >= 0 {field[y-1][x] += rem; if y == boundary[0] {boundary[0]-=1;}}
if x as isize - 1 >= 0 {field[y][x-1] += rem; if x == boundary[1] {boundary[1]-=1;}}
if y+1 < field.len() {field[y+1][x] += rem; if x == boundary[2]-1 {boundary[2]+=1;}}
if x+1 < field.len() {field[y][x+1] += rem; if y == boundary[3]-1 {boundary[3]+=1;}}
 
done = true;
}
}
}
 
done
}
 
// This function can be used to display the sandpile in the console window.
//
// Each row is mapped onto chars and those characters are then collected into a string.
// These are then printed to the console.
//
// Eg.: [0,1,1,2,3,0] -> [' ','░','░','▒','▓',' ']-> " ░░▒▓ "
fn display(field: &Vec<Vec<usize>>)
{
for row in field
{
let char_row = {
row.iter().map(|c| {match c {
0 => ' ',
1 => '░',
2 => '▒',
3 => '▓',
_ => '█'
}}).collect::<String>()
};
println!("{}", char_row);
}
}
 
// This function writes the end result to a file called "output.ppm".
//
// PPM is a very simple image format, however, it entirely uncompressed which leads to huge image sizes.
// Even so, for demonstrative purposes it's perfectly good to use. For something more robust, look into PNG libraries.
//
// Read more about the format here: http://netpbm.sourceforge.net/doc/ppm.html
fn write_pile(pile: &Vec<Vec<usize>>) {
use std::fs::File;
use std::io::Write;
 
// We first create the file (or erase its contents if it already existed).
let mut file = File::create("./output.ppm").unwrap();
 
// Then we add the image signature, which is "P3 <newline>[width of image] [height of image]<newline>[maximum value of color]<newline>".
write!(file, "P3\n{} {}\n255\n", pile.len(), pile.len()).unwrap();
 
for row in pile {
// For each row, we create a new string which has more or less enough capacity to hold the entire row.
// This is for performance purposes, but shouldn't really matter much.
let mut line = String::with_capacity(row.len() * 14);
 
// We map each value in the field to a color.
// These are just simple RGB values, 0 being the background, the rest being the "sand" itself.
for elem in row {
line.push_str(match elem {
0 => "100 40 15 ",
1 => "117 87 30 ",
2 => "181 134 47 ",
3 => "245 182 66 ",
_ => unreachable!(),
});
}
 
// Finally we write this string into the file.
write!(file, "{}\n", line).unwrap();
}
}
 
fn main() {
// This is how big the final image will be. Currently the end result would be a 16x16 picture.
let field_size = 16;
let mut playfield = vec![vec![0; field_size]; field_size];
 
// We put the initial sand in the exact middle of the field.
// This isn't necessary per se, but it ensures that sand can fully topple.
//
// The boundary is initially just the single tile which has the sand in it, however, as the algorithm
// progresses, this will grow larger too.
let mut boundary = [field_size/2-1, field_size/2-1, field_size/2, field_size/2];
playfield[field_size/2 - 1][field_size/2 - 1] = 16;
 
// This is the main loop. We update the field until it returns false, signalling that the pile reached its
// final state.
while advance(&mut playfield, &mut boundary) {};
 
// Once this happens, we simply display the result. Uncomment the line below to write it to a file.
// Calling display with large field sizes is not recommended as it can easily become too large for the console.
display(&playfield);
//write_pile(&playfield);
}

Output:

                
                
                
                
                
       ░        
      ▒░▒       
     ░░ ░░      
      ▒░▒       
       ░        
                
                
                
                
                
                

VBA[edit]

Sub SetupPile(a As Integer, b As Integer)
Application.ScreenUpdating = False
For i = 1 To a
For j = 1 To b
Cells(i, j).value = ""
Cells(i, j).Select
 
With Selection.Borders(xlEdgeLeft)
.LineStyle = xlContinuous
.Weight = xlMedium
End With
With Selection.Borders(xlEdgeTop)
.LineStyle = xlContinuous
.Weight = xlMedium
End With
With Selection.Borders(xlEdgeBottom)
.LineStyle = xlContinuous
.Weight = xlMedium
End With
With Selection.Borders(xlEdgeRight)
.LineStyle = xlContinuous
.Weight = xlMedium
End With
 
With Selection
.HorizontalAlignment = xlCenter
.VerticalAlignment = xlCenter
End With
 
Next j
Next i
Application.ScreenUpdating = True
End Sub
 
 
Sub Abelian_Sandpile()
Dim PileWidth As Integer
Dim PileHeight As Integer
Dim FieldArray() As Integer
 
Debug.Print "Start:" & Now()
 
'Set Size of Playing Field
PileWidth = 25
PileHeight = 25
 
ReDim FieldArray(PileWidth - 1, PileHeight - 1)
 
'Paint Basic Grid
SetupPile PileWidth, PileHeight
 
'Drop sand amount into middle of playing field
SandDropAmount = 1000
'Get around excel's incorrect rounding
SandDropColumn = Round((PileWidth / 2) + 0.001, 0)
SandDropRow = Round((PileHeight / 2) + 0.001, 0)
 
Cells(SandDropRow, SandDropColumn) = SandDropAmount
FieldArray(SandDropRow - 1, SandDropColumn - 1) = SandDropAmount
 
Continue = False
 
'Check if Pile is already stabilized at the start
For i = 1 To PileWidth 'Col
For j = 1 To PileHeight 'Row
If FieldArray(j - 1, i - 1) > 3 Then Continue = True
Next j
Next i
 
'While not stabilized
While Continue
For i = 1 To PileWidth
For j = 1 To PileHeight
If FieldArray(j - 1, i - 1) > 3 Then
'Reduce by 4
FieldArray(j - 1, i - 1) = FieldArray(j - 1, i - 1) - 4
'Increase Neighbours
't
If j >= 2 Then FieldArray(j - 2, i - 1) = FieldArray(j - 2, i - 1) + 1
'r
If i < PileWidth Then FieldArray(j - 1, i) = FieldArray(j - 1, i) + 1
'b
If j < PileHeight Then FieldArray(j, i - 1) = FieldArray(j, i - 1) + 1
'l
If i >= 2 Then FieldArray(j - 1, i - 2) = FieldArray(j - 1, i - 2) + 1
'Next round
GoTo Nextone
End If
Next j
Next i
 
Nextone:
 
'Check if now stabilized
Continue = False
For i = 1 To PileWidth
For j = 1 To PileHeight
'Paint every step if needed
'Cells(j, i) = FieldArray(j - 1, i - 1)
 
If FieldArray(j - 1, i - 1) > 3 Then Continue = True
Next j
Next i
 
Wend
 
'Print out final step
For i = 1 To PileWidth
For j = 1 To PileHeight
Cells(j, i) = FieldArray(j - 1, i - 1)
Next j
Next i
 
'Make field square and remove 0
Cells.Select
Selection.ColumnWidth = 2
Selection.RowHeight = 13.5
Selection.Replace What:="0", Replacement:="", LookAt:=xlPart, SearchOrder:=xlByRows, MatchCase:=False, SearchFormat:=False, ReplaceFormat:=False
Range("A1").Select
 
Range(Cells(1, 1), Cells(PileHeight, PileWidth)).Select
 
'Conditional Format
Selection.FormatConditions.AddColorScale ColorScaleType:=3
Selection.FormatConditions(Selection.FormatConditions.Count).SetFirstPriority
Selection.FormatConditions(1).ColorScaleCriteria(1).Type = xlConditionValueLowestValue
With Selection.FormatConditions(1).ColorScaleCriteria(1).FormatColor
.Color = 8109667
.TintAndShade = 0
End With
Selection.FormatConditions(1).ColorScaleCriteria(2).Type = xlConditionValuePercentile
Selection.FormatConditions(1).ColorScaleCriteria(2).value = 50
With Selection.FormatConditions(1).ColorScaleCriteria(2).FormatColor
.Color = 8711167
.TintAndShade = 0
End With
Selection.FormatConditions(1).ColorScaleCriteria(3).Type = xlConditionValueHighestValue
With Selection.FormatConditions(1).ColorScaleCriteria(3).FormatColor
.Color = 7039480
.TintAndShade = 0
End With
Range("A1").Select
 
Debug.Print "W,H,A:" & PileWidth & "," & PileHeight & "," & SandDropAmount
Debug.Print "End:" & Now()
 
End Sub

Output:

On Excel Page

Wren[edit]

Library: Wren-fmt
import "/fmt" for Fmt
 
class Sandpile {
// 'a' is a list of integers in row order
construct new(a) {
var count = a.count
_rows = count.sqrt.floor
if (_rows * _rows != count) Fiber.abort("The matrix of values must be square.")
_a = a
_neighbors = List.filled(count, 0)
for (i in 0...count) {
_neighbors[i] = []
if (i % _rows > 0) _neighbors[i].add(i-1)
if ((i + 1)%_rows > 0) _neighbors[i].add(i+1)
if (i - _rows >= 0) _neighbors[i].add(i-_rows)
if (i + _rows < count) _neighbors[i].add(i+_rows)
}
}
 
isStable { _a.all { |i| i <= 3 } }
 
// topples until stable
topple() {
while (!isStable) {
for (i in 0..._a.count) {
if (_a[i] > 3) {
_a[i] = _a[i] - 4
for (j in _neighbors[i]) _a[j] = _a[j] + 1
}
}
}
}
 
toString {
var s = ""
for (i in 0..._rows) {
for (j in 0..._rows) s = s + Fmt.swrite("$2d ", _a[_rows*i + j])
s = s + "\n"
}
return s
}
}
 
var printAcross = Fn.new { |str1, str2|
var r1 = str1.split("\n")
var r2 = str2.split("\n")
var rows = r1.count - 1
var cr = (rows/2).floor
for (i in 0...rows) {
var symbol = (i == cr) ? "->" : " "
Fmt.print("$s $s $s", r1[i], symbol, r2[i])
}
System.print()
}
 
var a1 = List.filled(25, 0)
a1[12] = 4
var a2 = List.filled(25, 0)
a2[12] = 6
var a3 = List.filled(25, 0)
a3[12] = 16
var a4 = List.filled(100, 0)
a4[55] = 64
for (a in [a1, a2, a3, a4]) {
var s = Sandpile.new(a)
var str1 = s.toString
s.topple()
var str2 = s.toString
printAcross.call(str1, str2)
}
Output:
 0  0  0  0  0      0  0  0  0  0 
 0  0  0  0  0      0  0  1  0  0 
 0  0  4  0  0  ->  0  1  0  1  0 
 0  0  0  0  0      0  0  1  0  0 
 0  0  0  0  0      0  0  0  0  0 

 0  0  0  0  0      0  0  0  0  0 
 0  0  0  0  0      0  0  1  0  0 
 0  0  6  0  0  ->  0  1  2  1  0 
 0  0  0  0  0      0  0  1  0  0 
 0  0  0  0  0      0  0  0  0  0 

 0  0  0  0  0      0  0  1  0  0 
 0  0  0  0  0      0  2  1  2  0 
 0  0 16  0  0  ->  1  1  0  1  1 
 0  0  0  0  0      0  2  1  2  0 
 0  0  0  0  0      0  0  1  0  0 

 0  0  0  0  0  0  0  0  0  0      0  0  0  0  0  0  0  0  0  0 
 0  0  0  0  0  0  0  0  0  0      0  0  0  0  0  0  0  0  0  0 
 0  0  0  0  0  0  0  0  0  0      0  0  0  0  1  2  1  0  0  0 
 0  0  0  0  0  0  0  0  0  0      0  0  0  2  2  2  2  2  0  0 
 0  0  0  0  0  0  0  0  0  0      0  0  1  2  2  2  2  2  1  0 
 0  0  0  0  0 64  0  0  0  0  ->  0  0  2  2  2  0  2  2  2  0 
 0  0  0  0  0  0  0  0  0  0      0  0  1  2  2  2  2  2  1  0 
 0  0  0  0  0  0  0  0  0  0      0  0  0  2  2  2  2  2  0  0 
 0  0  0  0  0  0  0  0  0  0      0  0  0  0  1  2  1  0  0  0 
 0  0  0  0  0  0  0  0  0  0      0  0  0  0  0  0  0  0  0  0