Temperature and time dependent pde coefficient, parabolic solver

Dear all,

I'm trying to implement a coefficient for a parabolic pde which is both time and temperature (solution) dependent.

For instance. d^2u/dx^2 + d^2u/dy^2 + coeff(t,u) = du/dt

Where u is the solution, t is time, d is the partial operator. The coeff(t,u) is a coefficient dependent on both time and solution. The problem is, coeff(t,u) is dependent on the previous time step of the solution. In the matlab solver parabolic, I can't figure out how to access the solution u for the previous time step in the solver (matlab makes it own time discretization while solving the pde).

I want to calculate something like:

coeff(t,u) = u(t-1) + u(t)

while the solver is running. Ideas?

[Torsten]

I can't imagine that coeff depends on the solution of the last time step. Otherwise, it were dependent on the size of the time step which must be nonsense.

Best wishes

Torsten.