[Bug Fix] Fix inplace op at backend (#546)

* Fix inplace operation

* fix line seprator

python/dgl/backend/mxnet/tensor.py

@@ -185,7 +185,7 @@ def unsorted_1d_segment_mean(input, seg_id, n_segs, dim):
     w = unsorted_1d_segment_sum(n_ones, seg_id, n_segs, 0)
     w = nd.clip(w, a_min=1, a_max=np.inf)
     y = unsorted_1d_segment_sum(input, seg_id, n_segs, dim)
-    y /= w.reshape((-1,) + (1,) * (y.ndim - 1))
+    y = y / w.reshape((-1,) + (1,) * (y.ndim - 1))
     return y
 
 def boolean_mask(input, mask):

python/dgl/backend/pytorch/tensor.py

@@ -157,7 +157,7 @@ def unsorted_1d_segment_mean(input, seg_id, n_segs, dim):
     w = unsorted_1d_segment_sum(th.ones_like(seg_id), seg_id, n_segs, 0).to(input)
     w = w.clamp(min=1)   # remove 0 entries
     y = unsorted_1d_segment_sum(input, seg_id, n_segs, dim)
-    y /= w.view((-1,) + (1,) * (y.dim() - 1))
+    y = y / w.view((-1,) + (1,) * (y.dim() - 1))
     return y
 
 def boolean_mask(input, mask):