[GitHub] jimmychou0704 opened a new issue #13748: custom loss cause "kernel died" in Jupyter notebook

[GitBox <gi...@apache.org>]

jimmychou0704 opened a new issue #13748: custom loss cause "kernel died" in Jupyter notebook
URL: https://github.com/apache/incubator-mxnet/issues/13748
 
 
   ## Description
   I am implementing mxnet SoftmaxOutput from scratch as a warm up for a more complicated custom loss function. However when I fit the model my jupyter notebook dies immediately. 
   
   ## Minimum reproducible example
   Here is how I defined my custom loss function,
   ```
   class MySoftmaxOutput(mx.operator.CustomOp):
   
       def forward(self, is_train, req, in_data, out_data, aux):
           numerator = mx.nd.exp(in_data[0] - mx.nd.max(in_data[0]))
           denominator = mx.nd.sum(numerator, axis = 1, keepdims=True)
           self.assign(out_data[0], req[0], mx.nd.divide(numerator,denominator))
   
       def backward(self, req, out_grad, in_data, out_data, in_grad, aux):
           #in_grad[0][:] = (out_data[0] - in_data[1])
           self.assign(in_grad[0], req[0], (out_data[0] - in_data[1]))
   
   @mx.operator.register('MySoftmaxOutput')
   class MySoftmaxOuptProp(mx.operator.CustomOpProp):
       
       def __init__(self):
           super(MySoftmaxOuptProp, self).__init__(need_top_grad=False)
   
       #Required.
       def list_arguments(self):
           return ['data', 'label'] 
   
       #Required.
       def infer_shape(self, in_shape):
           data_shape = in_shape[0]
           label_shape = (in_shape[0][0],)
           output_shape = in_shape[0]
           return [data_shape, label_shape], [output_shape], 
       def create_operator(self, ctx, shapes, dtypes):
           return MySoftmaxOutput()
   ```
   Then a model is constructed as following, 
   ```
   data = mx.sym.Variable('data')
   label = mx.sym.Variable('label')
   affine1 = mx.sym.FullyConnected(data=data,name='fc1',num_hidden=124)
   hidden1 = mx.sym.Activation(data=affine1, act_type='relu')
   affine2 = mx.sym.FullyConnected(data=data,name='fc2',num_hidden=2)
   out = mx.sym.Custom(data=affine2, label=label, name='softmax', op_type='MySoftmaxOutput')
   mod = mx.mod.Module(out, data_names=['data'], label_names=['label'], context=mx.cpu())
   mod.bind(data_shapes=nd_iter.provide_data, label_shapes=nd_iter.provide_label)
   mod.init_params(initializer=mx.init.Xavier())
   ```
   So far so good. But when I run` mod.fit(nd_iter, num_epoch=10, optimizer='adam')` my jupyter notebook died immediately. The data set I used is small (less than 10mb).
   ## What have you tried to solve it?
   
   1.  Used mx.sym.SoftmaxOutput then everything is working.
   

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