Add sanity check on seed in rng_mrg, to ensure the results' validity

theano/sandbox/rng_mrg.py

@@ -553,7 +553,7 @@ class GPU_mrg_uniform(mrg_uniform_base):
             {
                 PyErr_Format(PyExc_RuntimeError, "Cuda error: %%s: %%s.\\n", "mrg_uniform", cudaGetErrorString(err));
                 %(fail)s;
-            }                         
+            }
         }
 
         //////// </ code generated by mrg_uniform>
@@ -564,15 +564,31 @@ class MRG_RandomStreams(object):
 
     def __init__(self, seed=12345, use_cuda=None):
         """
-        :type seed: None or int
+        :type seed: int or list of 6 int.
+
+        :param seed: a default seed to initialize the random state.
+            If a single int is given, it will be replicated 6 times.
+            The first 3 values of the seed must all be less than M1 = 2147483647,
+            and not all 0; and the last 3 values must all be less than
+            M2 = 2147462579, and not all 0.
 
-        :param seed: a default seed to initialize the RandomState instances after build.  See
-        `RandomStreamsInstance.__init__` for more details.
         """
         super(MRG_RandomStreams, self).__init__()
         if isinstance(seed, int):
+            if seed == 0:
+                raise ValueError('seed should not be 0', seed)
+            elif seed >= M2:
+                raise ValueError('seed should be less than %i' % M2, seed)
             self.rstate = numpy.asarray([seed]*6, dtype='int32')
         elif len(seed)==6:
+            if seed[0] == 0 and seed[1] == 0 and seed[2] == 0:
+                raise ValueError('The first 3 values of seed should not be all 0', seed)
+            if seed[3] == 0 and seed[4] == 0 and seed[5] == 0:
+                raise ValueError('The last 3 values of seed should not be all 0', seed)
+            if seed[0] >= M1 or seed[1] >= M1 or seed[2] >= M1:
+                raise ValueError('The first 3 values of seed should be less than %i' % M1, seed)
+            if seed[3] >= M2 or seed[4] >= M2 or seed[5] >= M2:
+                raise ValueError('The last 3 values of seed should be less than %i' % M2, seed)
             self.rstate = numpy.asarray(seed, dtype='int32')
         else:
             raise TypeError("seed should be 1 integer or 6 integers")