Christophe Ortiz <[email protected]> writes: >> Does a shorter time step fix the oscillations? > > > Hi Jed, > > Thanks for the prompt reply. > > No, it did not in this case. However, I noticed for "smoother" cases that > max timestep matters. I try to fix it to finaltime/100 to avoid too large > timesteps. I also use -ts_adapt_basic_clip 0.1,1.1 to avoid large timesteps.
This just slows the rate of increasing time step. >> Is this with >> -ts_arkimex_type 1bee or something else? >> > > It occurs with 1bee, a2 or arkimex 3. Stick with 1bee until we understand better. >> Can you try -ts_arkimex_fully_implicit and add -snes_mf_operator if >> necessary to get SNES to converge? > > > > I tried -ts_arkimex_fully_implicit and it gave a wrong result. As if there > was no diffusion. Seems there is an artefact with fullyimplicit option. That does not sound right. Can you send a reproducible test case (best as a patch to PETSc)? > With -snes_mf_operator I got an error message: > [0]PETSC ERROR: No support for this operation for this object type! > [0]PETSC ERROR: Mat type mffd! ALWAYS, ALWAYS, ALWAYS send the ENTIRE error message! (Sorry about shouting, but I have to type this many times per day. Truncating error messages kills kittens!) >> (I'm assuming you have used an IMEX >> formulation here, but perhaps you already use fully implicit?) >> > > I put everything under IFunction and IJacobian. This part is not clear to > me actually. I understand that in IMEX methods, the LHS is solved > implicitely and the RHS explicitely. What happens when I use an IMEX method > with no RHS, everything in the LHS ? Is there any explicit stage ? No, if the RHS is empty, it should reduce to an implicit method. > Actually, I could solve the problem by adding mesh points. Since I start > from steep gaussian distributions with large peak values, maybe there was a > problem with large gradients. > > BTW, is it possible to have adaptive mesh in 1D with PETSc ? I am thinking > of steep profiles that evolve and that require a fine mesh at the beginning. You can do moving meshes (r-adaptivity) by writing coordinates as a coupled system. Or you can create a new grid and interpolate. You can use DMRefine and DMCoarsen.
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