I know how to modify in the upper menu, but I don’t know how to implement in code. By the way, does Octave have any functions for neural networks? Matlab’s sim functions and the like won’t work.

Question 1 : There is no straightforward way through code to change the font that the Octave GUI uses. There might be abstruse ways to find the GUI configuration file (a text file) on disk and manipulate that, but probably not a good idea.

Question 2 : “sim” is a function from the deep learning toolbox in Matlab. There is no equivalent toolbox yet for Octave.