Rosetta Code

Ramanujan's constant

Revision as of 04:18, 26 April 2019 by Wherrera (talk | contribs) (β†’β€Ž{{header|Julia}})

Calculate Ramanujan's constant (as described on the OEIS site) with at least 32 digits of precision, by the method of your choice. Optionally, if using the 𝑒**(Ο€*√x) approach, show that when evaluated with the last four Heegner numbers the result is almost an integer.

Ramanujan's constant is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Go

Library: bigfloat

The standard library's math/big.Float type lacks an exponentiation function and so I have had to use an external library to provide this function.

Also the math.Pi built in constant is not accurate enough to be used with big.Float and so I have used a more accurate string representation instead. <lang go>package main

import ( 

   "fmt"
   "github.com/ALTree/bigfloat"
   "math/big"

)

const ( 

   prec = 256 // say
   ps   = "3.1415926535897932384626433832795028841971693993751058209749445923078164"

)

func q(d int64) *big.Float { 

   pi, _Β := new(big.Float).SetPrec(prec).SetString(ps)
   tΒ := new(big.Float).SetPrec(prec).SetInt64(d)
   t.Sqrt(t)
   t.Mul(pi, t)
   return bigfloat.Exp(t)

}

func main() { 

   fmt.Println("Ramanujan's constant to 32 decimal places is:")
   fmt.Printf("%.32f\n", q(163))
   heegnersΒ := [4][2]int64{
       {19, 96},
       {43, 960},
       {67, 5280},
       {163, 640320},
   }
   fmt.Println("\nHeegner numbers yielding 'almost' integers:")
   tΒ := new(big.Float).SetPrec(prec)
   for _, hΒ := range heegners {
       qhΒ := q(h[0])
       cΒ := h[1]*h[1]*h[1] + 744
       t.SetInt64(c)
       t.Sub(t, qh)
       fmt.Printf("%3d: %51.32f β‰ˆ %18d (diff:Β %.32f)\n", h[0], qh, c, t)
   }

}</lang>

Output:
Ramanujan's constant to 32 decimal places is:
262537412640768743.99999999999925007259719818568888

Heegner numbers yielding 'almost' integers:
 19:             885479.77768015431949753789348171962682 β‰ˆ             885480 (diff: 0.22231984568050246210651828037318)
 43:          884736743.99977746603490666193746207858538 β‰ˆ          884736744 (diff: 0.00022253396509333806253792141462)
 67:       147197952743.99999866245422450682926131257863 β‰ˆ       147197952744 (diff: 0.00000133754577549317073868742137)
163: 262537412640768743.99999999999925007259719818568888 β‰ˆ 262537412640768744 (diff: 0.00000000000074992740280181431112)


Julia

<lang julia>

julia> a = BigFloat(MathConstants.e^(BigFloat(pi)))^(BigFloat(163.0)^0.5) - 262537412640768744 -7.499274028018143111206461436626630091372924626572825942241598957614307213309258e-13

julia> 262537412640768744 - a 2.625374126407687440000000000007499274028018143111206461436626630091372924626573e+17

</lang>

Perl

Translation of: Sidef

<lang perl>use strict; use warnings; use Math::AnyNum;

sub ramanujan_const { 

   my ($x, $decimals) = @_;

   $x = Math::AnyNum->new($x);
   my $prec = (Math::AnyNum->pi * $x->sqrt)/log(10) + $decimals + 1;
   local $Math::AnyNum::PREC = 4*$prec->round->numify;

   exp(Math::AnyNum->pi * $x->sqrt)->round(-$decimals)->stringify;

}

my $decimals = 100; printf("Ramanujan's constant to $decimals decimals:\n%s\n\n", 

   ramanujan_const(163, $decimals));

print "Heegner numbers yielding 'almost' integers:\n"; my @tests = (19, 96, 43, 960, 67, 5280, 163, 640320);

while (@tests) { 

   my ($h, $x) = splice(@tests, 0, 2);
   my $c = ramanujan_const($h, 32);
   my $n = Math::AnyNum::ipow($x, 3) + 744;
   printf("%3s: %51s β‰ˆ %18s (diff: %s)\n", $h, $c, $n, ($n - $c)->round(-32));

}</lang>

Output:
Ramanujan's constant to 100 decimals:
262537412640768743.9999999999992500725971981856888793538563373369908627075374103782106479101186073129511813461860645042

Heegner numbers yielding 'almost' integers:
 19:             885479.77768015431949753789348171962682 β‰ˆ             885480 (diff: 0.22231984568050246210651828037318)
 43:          884736743.99977746603490666193746207858538 β‰ˆ          884736744 (diff: 0.00022253396509333806253792141462)
 67:       147197952743.99999866245422450682926131257863 β‰ˆ       147197952744 (diff: 0.00000133754577549317073868742137)
163: 262537412640768743.99999999999925007259719818568888 β‰ˆ 262537412640768744 (diff: 0.00000000000074992740280181431112)

Perl 6

To generate a high-precision value for Ramanujan's constant, code is borrowed from three other Rosettacode tasks (with some modifications) for performing calculations of the value of Ο€, Euler's number, and integer roots. Additional custom routines for exponentiation are used to ensure all computations are done with rationals, specifically FatRats (rational numbers stored with arbitrary size numerator and denominator). The module Rat::Precise makes it simple to display these to a configurable precision. <lang perl6>use Rat::Precise;

  1. set the degree of precision for calculations

constant D = 54; constant d = 15;

  1. two versions of exponentiation where base and exponent are both FatRat

multi infix:<**> (FatRat $base, FatRat $exp where * >= 1 --> FatRat) { 

   2 R** $base**($exp/2);

}

multi infix:<**> (FatRat $base, FatRat $exp where * < 1 --> FatRat) { 

   constant Ξ΅ = 10**-D;
   my $low  = 0.FatRat;
   my $high = 1.FatRat;
   my $mid  = $high / 2;
   my $acc  = my $sqr = sqrt($base);

   while (abs($mid - $exp) > Ξ΅) {
     $sqr = sqrt($sqr);
     if ($mid <= $exp) { $low  = $mid; $acc *=   $sqr }
     else              { $high = $mid; $acc *= 1/$sqr }
     $mid = ($low + $high) / 2;
   }
   $acc.substr(0, D).FatRat;

}

  1. calculation of Ο€

sub Ο€ (--> FatRat) { 

   my ($a, $n) = 1, 1;
   my $g = sqrt 1/2.FatRat;
   my $z = .25;
   my $pi;

   for ^d {
       given [ ($a + $g)/2, sqrt $a * $g ] {
           $z -= (.[0] - $a)**2 * $n;
           $n += $n;
           ($a, $g) = @$_;
           $pi = ($a ** 2 / $z).substr: 0, 2 + D;
       }
   }
   $pi.FatRat;

}

multi sqrt(FatRat $r --> FatRat) { 

   FatRat.new: sqrt($r.nude[0] * 10**(D*2) div $r.nude[1]), 10**D;

}

  1. integer roots

multi sqrt(Int $n) { 

   my $guess = 10**($n.chars div 2);
   my $iterator = { ( $^x + $n div ($^x) ) div 2 };
   my $endpoint = { $^x == $^y|$^z };
   min ($guess, $iterator … $endpoint)[*-1, *-2];

}

  1. 'cosmetic' cover to upgrade input to FatRat sqrt

sub prefix:<√> (Int $n) { sqrt($n.FatRat) }

  1. calculation of 𝑒

sub postfix:<!> (Int $n) { (constant f = 1, |[\*] 1..*)[$n] } sub 𝑒 (--> FatRat) { sum map { FatRat.new(1,.!) }, ^D }

  1. inputs, and their difference, formatted decimal-aligned

sub format ($a,$b) { 

   sub pad ($s) { ' ' x ((34 - d - 1) - ($s.split(/\./)[0]).chars) }
   my $c = $b.precise(d, :z);
   my $d = ($a-$b).precise(d, :z);
   join "\n",
       (sprintf "%11s {pad($a)}%s\n", 'Int', $a) ~
       (sprintf "%11s {pad($c)}%s\n", 'Heegner', $c) ~
       (sprintf "%11s {pad($d)}%s\n", 'Difference', $d)

}

  1. override built-in definitions

constant Ο€ = &Ο€(); constant 𝑒 = &𝑒();

my $Ramanujan = 𝑒**(Ο€*√163); say "Ramanujan's constant to 32 decimal places:\nActual: " ~ 

   "262537412640768743.99999999999925007259719818568888\n" ~
   "Calculated: ", $Ramanujan.precise(32, :z), "\n";

say "Heegner numbers yielding 'almost' integers"; for 19, 96, 43, 960, 67, 5280, 163, 640320 -> $heegner, $x { 

   my $almost = 𝑒**(Ο€*√$heegner);
   my $exact  = $x**3 + 744;
   say format($exact, $almost);

}</lang>

Output:
Ramanujan's constant to 32 decimal places:
Actual:     262537412640768743.99999999999925007259719818568888
Calculated: 262537412640768743.99999999999925007259719818568888

Heegner numbers yielding 'almost' integers
        Int             885480
    Heegner             885479.777680154319498
 Difference                  0.222319845680502

        Int          884736744
    Heegner          884736743.999777466034907
 Difference                  0.000222533965093

        Int       147197952744
    Heegner       147197952743.999998662454225
 Difference                  0.000001337545775

        Int 262537412640768744
    Heegner 262537412640768743.999999999999250
 Difference                  0.000000000000750

REXX

Instead of calculating Β  e Β  and Β    Β  to some arbitrary length, Β  it was easier to just include those two constants with Β  201 Β  decimal digits Β  (which is the amount of decimal digits used for the calculations). Β  The results are displayed Β  (right justified) Β  with one half of that number of decimal digits. <lang rexx>/*REXX pgm displays Ramanujan's constant to at least 100 decimal digits of precision. */ d= min( length(pi()), length(e()) ) - length(.) /*calculate max #decimal digs supported*/ parse arg digs sDigs , 1 , , $ /*obtain optional arguments from the CL*/ if digs== | digs=="," then digs= d /*Not specified? Then use the default.*/ if sDigs== | sDigs=="," then sDigs= dΒ % 2 /* " " " " " " */ if $= | $="," then $= 19 43 67 163 /* " " " " " " */ 

digs= min( digs, d)                             /*the minimum decimal digs for calc.   */

sDigs= min(sDigs, d) /* " " " " display.*/ numeric digits digs /*inform REXX how many dec digs to use.*/ say "The value of Ramanujan's constant (calculated with " d say " decimal digits of precision, shown with " sDigs ' decimal digits):' say 

      do  j=1  for words($);     say            /*process each of the Heegner numbers. */
      #= word($, j)
      say 'When using the Heegner number: '  #  /*display which Heegner # is being used*/
      z= exp(pi * sqrt(#) )                     /*perform some heavy lifting here.     */
      say format(z, 25, sDigs)                  /*display a limited amount of dec digs.*/
      end   /*j*/

exit /*stick a fork in it, we're all done. */ /*──────────────────────────────────────────────────────────────────────────────────────*/ pi: pi= 3.1415926535897932384626433832795028841971693993751058209749445923078164062862, 

          || 089986280348253421170679821480865132823066470938446095505822317253594081284,
          || 8111745028410270193852110555964462294895493038196;     return pi

/*──────────────────────────────────────────────────────────────────────────────────────*/ e: e = 2.7182818284590452353602874713526624977572470936999595749669676277240766303535, 

          || 475945713821785251664274274663919320030599218174135966290435729003342952605,
          || 9563073813232862794349076323382988075319525101901;     return  e

/*──────────────────────────────────────────────────────────────────────────────────────*/ exp: procedure; parse arg x; ix= x%1; if abs(x-ix)>.5 then ix= ix + sign(x); x= x-ix 

      z=1;  _=1;   w=z;     do j=1; _= _*x/j;  z=(z+_)/1; if z==w  then leave;  w=z;  end
      if z\==0  then z= z * e() ** ix;                              return z/1

/*──────────────────────────────────────────────────────────────────────────────────────*/ root: procedure; parse arg x 1 ox,y 1 oy; if x=0 | y=1 then return x 

      _= sqrt(x);               if y<0  then _= 1 / _;          return _

/*──────────────────────────────────────────────────────────────────────────────────────*/ sqrt: procedure; parse arg x; if x=0 then return 0; d=digits(); i=; m.=9; h=d+6 

      numeric digits; numeric form;     if x<0  then  do;   x= -x;   i= 'i';   end
      parse value format(x, 2, 1, , 0)  'E0'   with   g  'E'  _ .;       g= g *.5'e'_Β % 2
         do j=0  while h>9;        m.j=h;                   h= hΒ % 2  +  1;    end  /*j*/
         do k=j+5  to 0  by -1;    numeric digits m.k;      g= (g+x/g) * .5;   end  /*k*/
      return g</lang>
output Β  when using the default inputs:
The value of Ramanujan's constant (calculated with  201
           decimal digits of precision, shown with  100  decimal digits):


When using the Heegner number:  19
                   885479.7776801543194975378934817196268207142865018553571526577110128809842286637202423189990118182067775711

When using the Heegner number:  43
                884736743.9997774660349066619374620785853768473991271391609175146278344881148747592189635643106023717101372606

When using the Heegner number:  67
             147197952743.9999986624542245068292613125786285081833125038167126333712821051229509988315235020413792423533706290

When using the Heegner number:  163
       262537412640768743.9999999999992500725971981856888793538563373369908627075374103782106479101186073129511813461860645042

Sidef

<lang ruby>func ramanujan_const(x, decimals=32) { 

   local Num!PREC = *"#{4*round((Num.pi*√x)/log(10) + decimals + 1)}"
   exp(Num.pi * √x) -> round(-decimals).to_s

}

var decimals = 100 printf("Ramanujan's constant to #{decimals} decimals:\n%s\n\n", 

    ramanujan_const(163, decimals))

say "Heegner numbers yielding 'almost' integers:" [19, 96, 43, 960, 67, 5280, 163, 640320].each_slice(2, {|h,x| 

   var c = ramanujan_const(h, 32)
   var n = (x**3 + 744)
   printf("%3s: %51s β‰ˆ %18s (diff: %s)\n", h, c, n, n-Num(c))

})</lang>

Output:
Ramanujan's constant to 100 decimals:
262537412640768743.9999999999992500725971981856888793538563373369908627075374103782106479101186073129511813461860645042

Heegner numbers yielding 'almost' integers:
 19:             885479.77768015431949753789348171962682 β‰ˆ             885480 (diff: 0.22231984568050246210651828037318)
 43:          884736743.99977746603490666193746207858538 β‰ˆ          884736744 (diff: 0.00022253396509333806253792141462)
 67:       147197952743.99999866245422450682926131257863 β‰ˆ       147197952744 (diff: 0.00000133754577549317073868742137)
163: 262537412640768743.99999999999925007259719818568888 β‰ˆ 262537412640768744 (diff: 0.00000000000074992740280181431112)
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