fix comments in cr;add inferred dimension test

Source/CNTKv2LibraryDll/Function.cpp

@@ -1287,7 +1287,7 @@ namespace CNTK
     FunctionPtr UnpackBatch(const Variable& operand, const std::wstring& name)
     {
         if (operand.DynamicAxes().size() > 1)
-            LogicError("UnpackBatch: only support input with batch axis itself.");
+            LogicError("UnpackBatch: only support input with batch axis and n sequence axis.");
 
         return UnaryOp(PrimitiveOpType::UnpackBatch, operand, Dictionary(), name);
     }

Source/CNTKv2LibraryDll/PrimitiveFunction.cpp

@@ -434,10 +434,8 @@ namespace CNTK
                                 InvalidArgument("AssignNode: Ref operand must be constant or parameter only.");
                             //delay the check for free dimension
                             if (m_inputs[0].Shape() != m_inputs[1].Shape() && 
-                                !m_inputs[0].Shape().HasFreeDimension() && 
-                                !m_inputs[1].Shape().HasFreeDimension() &&
-                                !m_inputs[0].Shape().HasInferredDimension() &&
-                                !m_inputs[1].Shape().HasInferredDimension())
+                                !m_inputs[0].Shape().HasUnboundDimension() && 
+                                !m_inputs[1].Shape().HasUnboundDimension())
                             {
                                 InvalidArgument("AssignNode: All inputs should have same sample layout.");
                             }

bindings/python/cntk/ops/tests/reshaping_test.py

@@ -516,3 +516,14 @@ def test_convert_dynamic_axis():
     z = y * 2
     expected = data.reshape((8, 3)) * 2
     assert np.array_equal(z.eval({x:data}), expected)
+
+    #test inferred dimension
+    x = C.input_variable((C.InferredDimension, 3))
+    const_x = C.unpack_batch(x)
+    assert len(const_x.dynamic_axes) == 0
+    assert const_x.shape == (C.FreeDimension, C.InferredDimension, 3)
+
+    const_y = const_x * 2
+    y = C.to_batch(const_y)
+    assert len(y.dynamic_axes) == 1
+    assert y.shape == (C.InferredDimension, 3)