[petsc-users] SNES_DIVERGED_LS_FAILURE

[Juha Jäykkä]

> Its hard to say anything without knowing what equations are being solved.

I was expecting that, but the equation is rather long to write in ascii. I do 
have a latex version somewhere that I can send if necessary. It is horribly 
nonlinear, though, including a term like (d/dx f) * (d^2/dx^2) f.

> However,
> does the linear problem converge? If so, you could try continuation in a
> parameter
> in the nonlinear term.

Linear solve is fine, it starts with (SNES iteration 1)
[0] KSPDefaultConverged(): Linear solver has converged. Residual norm 
8.93296e-12 is less than relative tolerance 1e-05 times initial right hand 
side norm 9.16829 at iteration 1

and goes to (SNES iteration 107 - which is the one which diverges)

[0] KSPDefaultConverged(): Linear solver has converged. Residual norm 
4.10794e-06 is less than relative tolerance 1e-05 times initial right hand 
side norm 1.07761 at iteration 1

Decreasing ksp_rtol to 1e-15 makes no difference, so I think the problem is 
not in the linear solve.

As to the continuation, I was trying to avoid that since I am already doing 
continuation in two parameters! That is because I am scanning a 2-dim 
parameter space. I know an exact solution for one pair of these two (namely, a 
straight line) and then start changing them always using the previous result 
as the new initial guess.

I will test the continuation in the worst nonlinear parts and see what 
happens.

Cheers,
-Juha

-- 
		 -----------------------------------------------
		| Juha Jäykkä, juhaj at iki.fi			|
		| http://www.maths.leeds.ac.uk/~juhaj		|
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