I'm solving a multiple component non-linear reaction-diffusion problem with
dealii and for time stepping I'm using the embedded explicit methods
available within the dealii framework.
If I understand the documentation correctly, the embedded method should
coarsen the time step if the error is less than the parameter 'coarsen_tol
This, however, does not seem to work! The error norm obtained by calling
get_status().error_norm on the embedded explicit runge kutta method returns
a value in the order of 1e-23(or even 0 for some methods) at all time
steps, while my coarsen tolerance is set to 1e-10. The time step for the
next iteration is still not coarsened, it always uses the initial time step
The way I implement the time stepping is exactly the same as the way it is
implemented in step 52 tutorial program. I would also like to mention that
the problem I'm solving is stiff and hence I'm using the embedded methods
for their ability to adapt step size.
The questions I have are as follows:
1. What is wrong with the embedded method? Does the problem lie in my
2. Are embedded methods(with small time steps) a good choice for stiff
problems or should I switch to an implicit method?
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