This tutorial explains a simple method to calculate RMSE in Python. ... the larger the difference between the predicted and observed values, which means the worse a model fits the data. ... the smaller the RMSE, the better a model is able to fit the data. It can be particularly useful to compare the RMSE of two different models with each other ...
It calculates the differences between the elements in your list, and returns a list that is one element shorter, which makes it unsuitable for plotting the derivative of a function. Loops in python are pretty slow (relatively speaking) but they are usually trivial to understand.