I have searched some useful questions and answers about how to solver bounded finite element function u, like 0 < u < 1. However, the demo contact-vi-snes indicated in these answers is stationary problem, my situation is time-dependent reaction-diffusion problem and the concentrations of several species need vector function u >= 0 at anytime.
First I change the concentration variables like c to exp(c), but I found this replacement increase the complexity and non-linearity of pdes.
I don't know how to modify the demo file to fit my problem, can anyone help me? Thanks!
