June 2018 Update

Task/Resistor-mesh/Modula-2/resistor-mesh.mod2

@@ -0,0 +1,111 @@
+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.