As pointed out by others, the blowup is an artifact of the visual representation, under-the-hood Theano does automatic differentiation (which they consider to b

As pointed out by others, the blowup is an artifact of the visual representation, under-the-hood Theano does automatic differentiation (which they consider to be an optimization on symbolic differentiation, which is why they keep calling it that): > In this way Theano can be used for doing efficient symbolic differentiation (as the expression returned by T.grad will be optimized during compilation), even for function with many inputs. (see automatic differentiation for a description of symbolic differentiation). http://deeplearning.net/software/theano/tutorial/gradients.html http://deeplearning.net/software/theano/tutorial/gradients.h...