When reproducing the results of the script 7_AE-RNN-end2endpaper for the FHN model, I came across this plot: <img width="1392" alt="image" src="https://user-images.githubusercontent.com/67231886/236514867-dbb069e3-3deb-47cc-abf7-5e6f5fd60419.png"> But I didn't find any explanations of these cost functions in the study. Could you tell me what each cost function seems to mean?