Hi, there: I met with some special problem when using adaptive time step. what I did is rather simple, using smaller dt when quantity F changed fast with time, and using larger dt when F changed slower with time. But everytime when I switched the dt, I have some oscilation in F, which is not there if using uniform dt.

BTW, I used the same adaptive method for my 1D codes, it worked. but for 2D, such problem comes. does anyone know how to solve the problem? I appreciate your advice and suggestions very much!

You are required to switch Dt smoothly in between, just as for grid.

I have tried to change it smoothly, but seems to me no much help. BTW, I use semi-implicit scheme, so that I need not to abide by the CFL limit. Is it true?