fix bug in nag optimizer

python/mxnet/optimizer/optimizer.py

@@ -974,10 +974,10 @@ def update(self, index, weight, grad, state):
         if state is not None:
             mom = state
             mom[:] *= self.momentum
-            grad += wd * weight
             mom[:] += grad
+            mom[:] += wd * weight
             grad[:] += self.momentum * mom
-            weight[:] += -lr * grad
+            weight[:] -= lr * grad
         else:
             assert self.momentum == 0.0
             weight[:] += -lr * (grad + wd * weight)

tests/python/unittest/test_optimizer.py

@@ -385,10 +385,10 @@ def update(self, index, weight, grad, state):
             else:
               mom = state
               mom[:] *= self.momentum
-              grad += wd * weight
               mom[:] += grad
+              mom[:] += wd * weight
               grad[:] += self.momentum * mom
-              weight[:] += -lr * grad
+              weight[:] -= lr * grad
         else:
             grad32 = array(grad, ctx=grad.context, dtype=np.float32)
             grad32 = grad32 * self.rescale_grad
@@ -400,10 +400,10 @@ def update(self, index, weight, grad, state):
                 weight32[:] += -lr * (grad32 + wd * weight32)
             else:
                 mom[:] *= self.momentum
-                grad32 += wd * weight32
                 mom[:] += grad32
+                mom[:] += wd * weight32
                 grad32[:] += self.momentum * mom
-                weight32[:] += -lr * grad32
+                weight32[:] -= lr * grad32
             tmp = weight32.astype(weight.dtype)
             tmp.copyto(weight)