I mean to say that non linear Schrodinger equation is derived already So i make my model on optisystem and with respect to my optisystem model i have changes in non linear schrodinger equation and simplify them. So I changes in non linear schrodinger equation according to my model so my queation is where integration or derivation should apply in my equation i don’t understand this thing. e:g in agrwal book their is present Split Step method to solve the equation and simplify them.