PyTorch vs TensorFlow -- spotting the difference

The best way to compare two frameworks is to code something up in both of them. I've written a companion jupyter notebook for this post and you can get it here. All code will be provided in the post too. First, let's code a simple approximator for the following function in both frameworks: We will try to find unknown parameter phi given data x and function values f(x). Yes, using stochastic gradient descent for this is an overkill and analytical solution may be found easily, but this problem will serve our purpose well as a simple example.