title: How to calculate the weight of a input in neural network
body: <p>After a neural network has been fully trained (suppose a normal feed forward network), if there a way to calculate how much weight one input has with respect to the final output? Note that I'm not talking about the weight for the input with respect to one neuron (that value should be calculated and adjusted by the NN during training process).</p>
  
  <p>For example if I have 3 inputs x1, x2 and x3, and I have one output y. After the network has been trained, can I know how much does x1 affect y? I guess it should be calculated by the partial derivative of y with respect to x1. But how do I know the non-linear function that the network represents? Is this possible at all?</p>
  
  <p>Thanks!</p>