The importance of the computation graph comes from the backward pass, which is used to compute the derivatives that we'll need for the weight update. In this example our goal is to compute the derivative of the output function L with respect to each of the input variables, i.e., ∂ L ∂ a , ∂ L ∂ b , and ∂ L ∂ c . The derivative ∂ L ∂ a , tells us how much a small change in a affects L.