fixed IncSubtensor.perform implementation for case of incrementing a single scalar

theano/tensor/basic.py

@@ -1935,7 +1935,12 @@ class IncSubtensor(Op):
         if not self.inplace:
             x = x.copy()
         sub_x = x.__getitem__(cdata)
-        sub_x += y
+        if sub_x.shape:
+            # we've sliced out an N-D tensor with N > 0
+            sub_x += y
+        else:
+            # scalar case
+            x.__setitem__(cdata, sub_x + y)
         out[0] = x
 
 def split(x, splits_size, n_splits, axis=0):

theano/tensor/tests/test_basic.py

@@ -852,7 +852,10 @@ class T_subtensor(unittest.TestCase):
         n = as_tensor_variable(data)
         t = n[1,0]
         gn = grad(sum(exp(t)), n)
-        gval = eval_outputs([gn])
+        f = function([], gn, mode=None)
+        print 'toposort', f.maker.env.toposort()
+        gval = f()
+        print gval
         good = numpy.zeros_like(data)
         good[1,0] = numpy.exp(data[1,0])
         self.failUnless(numpy.all(gval == good), (gval, good))