Resistor mesh: Difference between revisions
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<pre>1.608991241730729655954495520510088761201</pre>
=={{header|Modula-2}}==
<lang modula>MODULE ResistorMesh;
FROM RConversions IMPORT RealToStringFixed;
FROM Terminal IMPORT WriteString,WriteLn,ReadChar;
CONST S = 10;
TYPE Node = RECORD
v : LONGREAL;
fixed : INTEGER;
END;
PROCEDURE SetBoundary(VAR m : ARRAY OF ARRAY OF Node);
BEGIN
m[1][1].v := 1.0;
m[1][1].fixed := 1;
m[6][7].v := -1.0;
m[6][7].fixed := -1;
END SetBoundary;
PROCEDURE CalcDiff(VAR m,d : ARRAY OF ARRAY OF Node) : LONGREAL;
VAR
total,v : LONGREAL;
i,j,n : INTEGER;
BEGIN
total := 0.0;
FOR i:=0 TO S DO
FOR j:=0 TO S DO
v := 0.0;
n := 0;
IF i>0 THEN
v := v + m[i-1][j].v;
INC(n);
END;
IF j>0 THEN
v := v + m[i][j-1].v;
INC(n);
END;
IF i+1<S THEN
v := v + m[i+1][j].v;
INC(n);
END;
IF j+1<S THEN
v := v + m[i][j+1].v;
INC(n);
END;
v := m[i][j].v - v / LFLOAT(n);
d[i][j].v := v;
IF m[i][j].fixed=0 THEN
total := total + v*v;
END;
END;
END;
RETURN total;
END CalcDiff;
PROCEDURE Iter(m : ARRAY OF ARRAY OF Node) : LONGREAL;
VAR
d : ARRAY[0..S] OF ARRAY[0..S] OF Node;
i,j,k : INTEGER;
cur : ARRAY[0..2] OF LONGREAL;
diff : LONGREAL;
BEGIN
FOR i:=0 TO S DO
FOR j:=0 TO S DO
d[i][j] := Node{0.0,0};
END;
END;
diff := 1.0E10;
WHILE diff>1.0E-24 DO
SetBoundary(m);
diff := CalcDiff(m,d);
FOR i:=0 TO S DO
FOR j:=0 TO S DO
m[i][j].v := m[i][j].v - d[i][j].v;
END;
END;
END;
FOR i:=0 TO S DO
FOR j:=0 TO S DO
k:=0;
IF i#0 THEN INC(k) END;
IF j#0 THEN INC(k) END;
IF i<S-1 THEN INC(k) END;
IF j<S-1 THEN INC(k) END;
cur[m[i][j].fixed+1] := cur[m[i][j].fixed+1] + d[i][j].v*LFLOAT(k);
END;
END;
RETURN (cur[2]-cur[0]) / 2.0;
END Iter;
VAR
mesh : ARRAY[0..S] OF ARRAY[0..S] OF Node;
buf : ARRAY[0..32] OF CHAR;
r : LONGREAL;
pos : CARDINAL;
ok : BOOLEAN;
BEGIN
pos := 0;
r := 2.0 / Iter(mesh);
WriteString("R = ");
RealToStringFixed(r, 15,0, buf, pos, ok);
WriteString(buf);
WriteString(" ohms");
WriteLn;
ReadChar;
END ResistorMesh.</lang>
=={{header|Octave}}==
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