make C square

Sketch.py

@@ -29,8 +29,9 @@ class Sketch(object):
                     shape_vars[shape_var] = varid
                     varid += 1
                     varid_to_shape_var.append(shape_var)
-        C = zeros((len(equations), len(shape_vars)))
-        d = zeros(len(equations))
+        dim = max(len(equations), len(shape_vars))
+        C = zeros((dim, dim))
+        d = zeros(dim)
         for i in range(len(equations)):
             e = equations[i]
             coeffs = e[0]