How to get mathematical expression of input and target in artificial neural network

I have four input vectors of (1*36) matrix each and one output vector (1*36). I want to develop a coding using ANN which not only process and train the network but displays how processing is going on i.e. calculated value of mse and R at each epoch. At last the code should generate a mathematical expression of how output vector is related to input vector.Network is simple curve fitting network given in tutorials. Any sort of help will be appreciated.