Added another exact function, this time from scipy website

interp/tools.py

@@ -49,6 +49,10 @@ def friendly_exact_3D(X):
   x,y,z = X
   return 1 + x*x + y*y + z*z
 
+def scipy_exact_2D(X):
+  x,y = X
+  return x*(1-x)*np.cos(4*np.pi*x) * np.sin(4*np.pi*y**2)**2
+
 def improved_answer(answer, exact):
   if not answer['error']:
     # was probably just a linear interpolation