[GitHub] [incubator-mxnet] apeforest edited a comment on issue #15120: [bug] fix higher grad log

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apeforest edited a comment on issue #15120: [bug] fix higher grad log 
URL: https://github.com/apache/incubator-mxnet/pull/15120#issuecomment-499170409
 
 
   @kshitij12345 I have some question about the equation `expected_head_grad = (grad_op(x) * head_grad_grads).asnumpy()` in your test.
   
   My understanding from the chain rule:
   
   ```
   Given y =f(x)
   dL/dx = dL/dy * dy/dx -->  this is the first forward pass. Let dL/dy be y_grad, we get dL/dx (noted as x_grad)
   
   Now we rewrite the above the equation:
   
   input0: y_grad
   input1: x
   output: x_grad = y_grad * f'(x)
   
   Another backward pass for this would be:
   dL/d y_grad = dL/d x_grad * f'(x)
   dL/dx = dL/d x_grad * y_grad * f''(x)
   
   What is the meaning of dL/d y_grad? Are we treating y_grad as another input variable here?
   ```
   
   Thanks for your clarification.
   
   

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