[petsc-users] snes failures

[Juha Jaykka]

> not. This usually indicates a bad guess for Newton. I would now advocate

Oh, did I forget to mention, that other initial conditions DO converge. The 
funny thing is the initial condition which does NOT converge is actually 
CLOSER to the solution than ones which DO. Had it been the other way around, I 
probably would not have thought twice of it.

>   1) Grid sequencing: This is easy if you use a DMDA. You just use
> -snes_grid_sequence
>       and its automatic. Since you report that smaller grids converge, this
> is usually enough.

Unfortunately, no.

>   2) NPC: If the above fails, I would try preconditioning Newton with GS.
> You can do this
>       just using multiplicative composition, or left preconditioning.

I'm not sure what you mean here. Do you mean I should run normal newton line 
search snes with SNESSetNPC(snes_of_type_gs)?

If so, does the inner snes_of_type_gs and the outer snes_of_type_newtonls get 
all the same routines? I guess so, but just checking.

> If 1 works, then its likely that FAS would work even better.

I wish it was so easy: I did try all the snes types before posting the first 
post. Also all KSP types. Except those that need things I don't have, of 
course.

Cheers,
Juha
-------------- next part --------------
A non-text attachment was scrubbed...
Name: signature.asc
Type: application/pgp-signature
Size: 819 bytes
Desc: This is a digitally signed message part.
URL: <http://lists.mcs.anl.gov/pipermail/petsc-users/attachments/20160520/f50b24f3/attachment.pgp>