make tensor.outer(x,y) work when ndim != 1 as numpy.outer.

theano/tensor/basic.py

@@ -8185,7 +8185,14 @@ def tensordot(a, b, axes=2):
 
 
 def outer(x, y):
-    """Return vector-vector outer product."""
+    """Return vector-vector outer product.
+
+    If an input isn't a vector, we flatten it first.
+    """
+    if x.ndim != 1:
+        x = x.flatten()
+    if y.ndim != 1:
+        y = y.flatten()
     return dot(
             x.dimshuffle(0, 'x'),
             y.dimshuffle('x', 0))

theano/tensor/tests/test_basic.py

@@ -2729,6 +2729,21 @@ class T_min_max(unittest.TestCase):
         #axis=1)[0], n)),axis=1)
 
 
+class T_outer(unittest.TestCase):
+    def test_outer(self):
+        for m in range(4):
+            for n in range(4):
+                x = tensor.tensor(dtype='floatX', broadcastable=(False,) * m)
+                y = tensor.tensor(dtype='floatX', broadcastable=(False,) * n)
+                s1 = numpy.random.randint(1, 10, m)
+                s2 = numpy.random.randint(1, 10, n)
+                v1 = numpy.asarray(numpy.random.rand(*s1)).astype(floatX)
+                v2 = numpy.asarray(numpy.random.rand(*s2)).astype(floatX)
+                print m, n, s1, s2
+                o = tensor.outer(x, y).eval({x: v1, y: v2})
+                assert_allclose(o, numpy.outer(v1, v2))
+
+
 class T_subtensor(unittest.TestCase, utt.TestOptimizationMixin):
     """
     This is build in a way that allow to reuse it to test the