On Jun 26, 2019, at 4:17 PM, Manuel Valera via petsc-users
<[email protected]<mailto:[email protected]>> wrote:
Hi PETSc,
I am trying to implement the Time stepping routines in my model, i have a
working runge-kutta time scheme that goes to the following steps:
* Interpolate u,v,w to the time advancing variable position.
* Calculate nonlinear coefficients and advect velocities with a
forward-backward shock capturing scheme.
* Calculate the variable laplacian
* Sum terms to create RHS (nonlinear advected velocities + laplacian)
* Finally, the runge kutta integration is done in a typical way that looks
like:
newtemp(t+1) = prevtemp(t) + dt*RHS
So my questions are:
* I think my problem is nonlinear, but is being made linearized by the
advecting scheme, is this correct? this is to know if i should use the linear
or nonlinear routines for TS.
TSComputeRHSFunctionLinear is just a convenience function for linear ODEs in
the form udot=Au. Using it won’t buy you much. So for TS starters, it is fine
to assume your problem is nonlinear and think of the form udot=f(t,u) where f
is the RHS function.
* How do i know what are the appropriate routines i should be using here?
so far i think i should use the following:
call TSCreate(PETSC_COMM_WORLD,ts,ierr)
call TSSetProblemType(ts,TS_LINEAR,ierr)
call TSSetTimeStep(ts,dt,ierr)
call TSSetFromOptions(ts,ierr)
call TSSetRHSFunction(ts,NULL,TSComputeRHSFunctionLinear,NULL,ierr)
call TSSolve(ts,loctemperature,ierr)
Should i use call TSSetRHSJacobian for the temperature jacobian in this case?
I would suggest to write your own RHSFunction and set it to TS with
TSSetRHSFunction().
I am using
https://www.mcs.anl.gov/petsc/petsc-current/src/ts/examples/tutorials/ex4.c.html
as a general guide, is there a more appropriate example?
ex4 is a good example. In addition, ex9 uses finite volume method with slope
limiters to solve a variety of problems such as advection equation, burgers
equation and shallow water equation. It might be an overkill, but it seems to
be close to the problem you are trying to solve. Note that you might want to
use the SSP methods (-ts_type ssp) instead of the classic Runge-Kutta methods
for problems with shocks.
Hong (Mr.)
The dt value and total timesteps are controlled by the model,
Thanks for your help,
