Fix bug in patternbroadcast with empty pattern

theano/tensor/basic.py

@@ -4079,7 +4079,7 @@ class Rebroadcast(Op):
             broadcast_pattern[k] = str(int(v))
         return '%s{%s}' % (self.__class__.__name__, ','.join(broadcast_pattern))
     def make_node(self, x):
-        if x.ndim <= numpy.max(self.axis.keys()):
+        if self.axis.keys() and (x.ndim <= numpy.max(self.axis.keys())):
             raise ValueError('Trying to rebroadcast nonexistant dimension')
         t = x.type.__class__(dtype = x.type.dtype,
                        broadcastable = [self.axis.get(i, b)

theano/tensor/tests/test_basic.py

@@ -34,7 +34,7 @@ from theano.tensor import (_shared, wvector, bvector, autocast_float_as,
         get_constant_value, ivector, reshape, scalar_from_tensor, scal,
         iscalars, arange,  dscalars, fvector, imatrix, numeric_grad,
         opt, ComplexError, TensorDot, lvector, true_div, max, min, Split, roll,
-        tile)
+        tile, patternbroadcast)
 from theano.tests import unittest_tools as utt
 
 
@@ -5267,6 +5267,15 @@ class test_broadcast(unittest.TestCase):
         assert addbroadcast(unbroadcast(x,1),0).owner.inputs[0] is x
         assert addbroadcast(unbroadcast(x,0),0) is x
 
+    def test_patternbroadcast(self):
+        # Test that patternbroadcast with an empty broadcasting pattern works
+        x = scalar('x')
+        m = tensor.matrix('m')
+        s = patternbroadcast(m, x.broadcastable)
+        assert s is m
+        x2 = patternbroadcast(x, x.broadcastable)
+        assert x2 is x
+
     def test_infer_shape(self):
         x = matrix()
         y = addbroadcast(x, 0)