Resistor mesh: Difference between revisions

=={{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>