Merge pull request #482 from QuantEcon/sp_linalg

FIX: Import scipy.sparse.linalg

Author: oyamad

quantecon/markov/ddp.py

@@ -417,7 +417,8 @@ def s_wise_max(vals, out=None, out_argmax=None):
 
         # Linear equation solver to be used in evaluate_policy
         if self._sparse:
-            self._lineq_solve = sp.linalg.spsolve
+            import scipy.sparse.linalg
+            self._lineq_solve = scipy.sparse.linalg.spsolve
             self._I = sp.identity(self.num_states, format='csr')
         else:
             self._lineq_solve = np.linalg.solve