[petsc-users] KSPBuildSolution

[Juha Jäykkä]

Hi again.

I do not know which one to answer to, but thanks to all. I got one step 
further with your help:

[0]PETSC ERROR: Zero pivot row 1 value 1.90611e-13 tolerance 1e-12!

Adding -pc_factor_shift_type POSITIVE_DEFINITE helps and now I get at least 
some progress. It does not matter if I use -snes_fd, coloring or my hand-
written Jacobian. If I start from a non-solution initial guess, they all 
progress somewhat towards what I believe is more or less a real solution. This 
is all ran with -pc_type lu -ksp_type preonly, btw.

However, they do not seem to change the second to the last (counting from left 
to right) value on the lattice (this is 1D). It does change, but only by 0.02% 
while values elsewhere in the lattice change much more significantly. Again, I 
am running with the parameters where I know the exact solution and my initial 
guess is, on purpose, 0.01 off the correct one (except at the endpoints). What 
could be causing this?

One thing strikes me as odd. I tried checking the value of the function at the 
first iteration and at that particular point it is of the order of -1.e-9, 
whereas in the next point to the left, it is +1.e-9 and then starts increasing 
towards the left before it starts decreasing again around half-way through the 
lattice.

Cheers,
Juha

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