refine square_error_cost layer (#5216)

* reimplement pow operator

* add pow_grad operator

* fix code style

* fix build error

* fix op_test bug

* revert pow operator

* add FIXME comment

Author: QiJune

paddle/operators/activation_op.h

@@ -547,6 +547,7 @@ struct ELUGradFunctor : public BaseActivationFunctor<T> {
   }
 };
 
+// FIXME(qijun) https://github.com/PaddlePaddle/Paddle/issues/5198
 template <typename T>
 struct PowFunctor : public BaseActivationFunctor<T> {
   float factor;

python/paddle/v2/framework/layers.py

@@ -225,10 +225,7 @@ def square_error_cost(input, label, **kwargs):
 
     square_out = helper.create_tmp_variable(dtype=input.data_type)
     helper.append_op(
-        type='pow',
-        inputs={'X': [minus_out]},
-        outputs={'Y': [square_out]},
-        attrs={'factor': 2.0})
+        type='square', inputs={'X': [minus_out]}, outputs={'Y': [square_out]})
     return square_out
 
 

python/paddle/v2/framework/tests/op_test.py

@@ -281,7 +281,8 @@ def find_actual(target_name, fetch_list):
                                          type(sub_out))
                 for sub_out_name, expect in sub_out:
                     idx = find_actual(sub_out_name, fetch_list)
-                    actual_t = np.array(outs[idx])
+                    actual = outs[idx]
+                    actual_t = np.array(actual)
                     expect_t = expect[0] \
                         if isinstance(expect, tuple) else expect
                     self.assertTrue(
@@ -291,19 +292,20 @@ def find_actual(target_name, fetch_list):
                         str(place))
                     if isinstance(expect, tuple):
                         self.assertListEqual(
-                            actual_t.lod(), expect[1], "Output (" + sub_out_name
-                            + ") has different lod at " + str(place))
+                            actual.lod(), expect[1], "Output (" + sub_out_name +
+                            ") has different lod at " + str(place))
             else:
                 idx = find_actual(out_name, fetch_list)
-                actual_t = outs[idx]
+                actual = outs[idx]
+                actual_t = np.array(actual)
                 expect = self.outputs[out_name]
                 expect_t = expect[0] if isinstance(expect, tuple) else expect
                 self.assertTrue(
                     np.allclose(
                         actual_t, expect_t, atol=atol),
                     "Output (" + out_name + ") has diff at " + str(place))
                 if isinstance(expect, tuple):
-                    self.assertListEqual(actual_t.lod(), expect[1],
+                    self.assertListEqual(actual.lod(), expect[1],
                                          "Output (" + out_name +
                                          ") has different lod at " + str(place))