!3711 fix topK multi dimention grad func

Merge pull request !3711 from fangzehua/topkgrad

mindspore/ops/_grad/grad_nn_ops.py

@@ -14,6 +14,7 @@
 # ============================================================================
 
 """Define the grad rules of neural network related operations."""
+import math
 import numpy as np
 from mindspore.ops import _selected_grad_ops as SG
 from mindspore.ops.primitive import constexpr
@@ -628,19 +629,62 @@ def get_bprop_onehot(self):
     return bprop
 
 
+@constexpr
+def _range_op(start, limit, delta, dtype):
+    """helper function for Grad TopK"""
+    range_op = inner.Range(float(start), float(limit), float(delta))
+    length_input = math.ceil((limit - start) / delta)
+    input_tensor = Tensor(list(range(length_input)), dtype)
+    range_out = range_op(input_tensor)
+    return range_out
+
+@constexpr
+def _get_1d_shape(in_shape):
+    """helper function for Grad TopK"""
+    out_shape = 1
+    for i in in_shape:
+        out_shape *= i
+    return (out_shape,)
+
 @bprop_getters.register(P.TopK)
 def get_bprop_top_kv2(self):
     """Grad definition for `TopK` operation."""
     scatter = P.ScatterNd()
     expand_dims = P.ExpandDims()
     shape_op = P.Shape()
+    reshape_op = P.Reshape()
+    dtype = P.DType()
 
     def bprop(input_x, k, out, dout):
+
+        # (n1, n2, ...., n_p), in_lastdim = n_p
+        in_shape = shape_op(input_x)
+        in_lastdim = in_shape[-1]
+
+        # (n_1, ... n_(p-1), k), ind_lastdim = k
         indices = out[1]
-        indices = expand_dims(indices, -1)
-        updates = dout[0]
-        shapes = shape_op(input_x)
-        return scatter(indices, updates, shapes), zeros_like(k)
+        ind_shape = shape_op(indices)
+        ind_lastdim = ind_shape[-1]
+
+        # (n_1*n_2..*n_(p-1), k),  outerdim = n_1*n_2..*n_(p-1)
+        ind_2d = reshape_op(indices, (-1, ind_lastdim))
+        outerdim = shape_op(ind_2d)[0]
+
+        # [0, outterdim, 2*outerdim, ..., (k-1)*outerdim]
+        indices_dtype = dtype(indices)
+        range_flatten_index = _range_op(0, outerdim * in_lastdim, in_lastdim, indices_dtype)
+
+        # expand_dims to (k, 1), then broadcast
+        ind = reshape_op(ind_2d + expand_dims(range_flatten_index, -1), (-1,))
+        in_shape_1d = _get_1d_shape(in_shape)
+
+        out_grad = reshape_op(
+            scatter(
+                expand_dims(ind, -1),
+                reshape_op(dout[0], (-1,)),
+                in_shape_1d),
+            in_shape)
+        return out_grad, zeros_like(k)
 
     return bprop