Fix issue with renamed function in the tutorial notebook.

This MR resolves Issue #90 (closed). A function has been renamed and therefore causes an error when it is called in a tutorial notebook, specifically the polynomial regression.

PS: In the near future, the regression will be updated and the interface will be changed as well. In particular, the regression matrix will not be manually constructed using the evaluation of the Newton form of the Lagrange monomials. This was considered a workaround to deal with regression before a separate regression module is available.