NetPortGradient

NetPortGradient["port"] represents the gradient of the output of a net with respect to the value of the specified input port. 

NetPortGradient["param"] represents the gradient of the output with respect to a learned parameter named param.

NetPortGradient[{layer1,layer2,…,"param"}] represents the gradient with respect to a parameter at a specific position in a net.

NetPortGradient[All] represents the gradients with respect to all inputs and parameters.

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