tasks a-s

Task/Resistor-mesh/C/resistor-mesh.c

@@ -0,0 +1,65 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+#define S 10
+typedef struct { double v; int fixed; } node;
+
+#define each(i, x) for(i = 0; i < x; i++)
+node **alloc2(int w, int h)
+{
+	int i;
+	node **a = calloc(1, sizeof(node*)*h + sizeof(node)*w*h);
+	each(i, h) a[i] = i ? a[i-1] + w : (node*)(a + h);
+	return a;
+}
+
+void set_boundary(node **m)
+{
+	m[1][1].fixed =  1; m[1][1].v =  1;
+	m[6][7].fixed = -1; m[6][7].v = -1;
+}
+
+double calc_diff(node **m, node **d, int w, int h)
+{
+	int i, j, n;
+	double v, total = 0;
+	each(i, h) each(j, w) {
+		v = 0; n = 0;
+		if (i) v += m[i-1][j].v, n++;
+		if (j) v += m[i][j-1].v, n++;
+		if (i+1 < h) v += m[i+1][j].v, n++;
+		if (j+1 < w) v += m[i][j+1].v, n++;
+
+		d[i][j].v = v = m[i][j].v - v / n;
+		if (!m[i][j].fixed) total += v * v;
+	}
+	return total;
+}
+
+double iter(node **m, int w, int h)
+{
+	node **d = alloc2(w, h);
+	int i, j;
+	double diff = 1e10;
+	double cur[] = {0, 0, 0};
+
+	while (diff > 1e-24) {
+		set_boundary(m);
+		diff = calc_diff(m, d, w, h);
+		each(i,h) each(j, w) m[i][j].v -= d[i][j].v;
+	}
+
+	each(i, h) each(j, w)
+		cur[ m[i][j].fixed + 1 ] += d[i][j].v *
+				(!!i + !!j + (i < h-1) + (j < w -1));
+
+	free(d);
+	return (cur[2] - cur[0])/2;
+}
+
+int main()
+{
+	node **mesh = alloc2(S, S);
+	printf("R = %g\n", 2 / iter(mesh, S, S));
+	return 0;
+}