Sketch.solve(): explicitly initialize vars to 0.0

Sketch.py

@@ -30,6 +30,10 @@ class Sketch(object):
                     varid_to_shape_var.append(shape_var)
         C = empty((len(equations), len(shape_vars)))
         d = empty(len(equations))
+        for row in range(len(equations)):
+            for col in range(len(shape_vars)):
+                C[row][col] = 0.0
+            d[row] = 0.0
         for i in range(len(equations)):
             e = equations[i]
             coeffs = e[0]