MATLAB: Reg. PDEPE ‘s internal discretization of time

Question

Hello, I am solving a reaction diffusion equation where there is a radiation term. Now the radiation is given once per day let's say instantaneously. But instead of modelling this instantaneous radiation I took time step to be one day. And modelling the radiation only as a function of space(or x). So I would expect this radiation term to be counted only once and would be equivalent to instantaneous radiation. But I came to know from someone that while solving the problem pdepe might be discretizing time in it's own way during the simulation. Is this so? If this is so then I am in trouble since the radiation term would no longer be counted only once and I would end up giving an overdose. Can someone please shed some light on how pdepe discretizes time internally over and above the discretization I specify? Thanks

Answer 1

pdepe uses the variable time step ODE solver, ode15s, internally.

http://www.mathworks.com/help/matlab/ref/ode15s.html

The time step size is automatically chosen by ode15s to obtain a prescribed accuracy.

The time discretization that you specify to the pdepe function is only to tell ode15s the points in time where you would like output.

Bill