tasks a-s

Task/Resistor-mesh/Python/resistor-mesh.py

@@ -0,0 +1,64 @@
+DIFF_THRESHOLD = 1e-40
+
+class Fixed:
+    FREE = 0
+    A = 1
+    B = 2
+
+class Node:
+    __slots__ = ["voltage", "fixed"]
+    def __init__(self, v=0.0, f=Fixed.FREE):
+        self.voltage = v
+        self.fixed = f
+
+def set_boundary(m):
+    m[1][1] = Node( 1.0, Fixed.A)
+    m[6][7] = Node(-1.0, Fixed.B)
+
+def calc_difference(m, d):
+    h = len(m)
+    w = len(m[0])
+    total = 0.0
+
+    for i in xrange(h):
+        for j in xrange(w):
+            v = 0.0
+            n = 0
+            if i != 0:  v += m[i-1][j].voltage; n += 1
+            if j != 0:  v += m[i][j-1].voltage; n += 1
+            if i < h-1: v += m[i+1][j].voltage; n += 1
+            if j < w-1: v += m[i][j+1].voltage; n += 1
+            v = m[i][j].voltage - v / n
+
+            d[i][j].voltage = v
+            if m[i][j].fixed == Fixed.FREE:
+                total += v ** 2
+    return total
+
+def iter(m):
+    h = len(m)
+    w = len(m[0])
+    difference = [[Node() for j in xrange(w)] for i in xrange(h)]
+
+    while True:
+        set_boundary(m) # Enforce boundary conditions.
+        if calc_difference(m, difference) < DIFF_THRESHOLD:
+            break
+        for i, di in enumerate(difference):
+            for j, dij in enumerate(di):
+                m[i][j].voltage -= dij.voltage
+
+    cur = [0.0] * 3
+    for i, di in enumerate(difference):
+        for j, dij in enumerate(di):
+            cur[m[i][j].fixed] += (dij.voltage *
+                (bool(i) + bool(j) + (i < h-1) + (j < w-1)))
+
+    return (cur[Fixed.A] - cur[Fixed.B]) / 2.0
+
+def main():
+    w = h = 10
+    mesh = [[Node() for j in xrange(w)] for i in xrange(h)]
+    print "R = %.16f" % (2 / iter(mesh))
+
+main()