[petsc-users] KSPBuildSolution

[Juha Jäykkä]

> Yes, if your BC do not give at least a locally unique solution, then your
> Jacobian will
> be rank deficient and Newton breaks down. You can still try Picard, but I
> recommend
> understanding what you mean by a solution first.

Thanks for confirming. And for the suggestion to try Picard, but it simply 
shoots out to somewhere in the direction of Alpha Centauri or some such: 
reaches function values in excess of 1.e+34 in less than ten SNES 
iterations... Perhaps there is such a solution, but that is certainly not what 
I want.

Especially since I think I figured out an alternative boundary condition. But 
I do not know how to implement that in PETSc.

How do I require

f'(xmax) = constant_A
f(xmax) = constant_B

and no condition (I could require f(xmin)=0, but that is exactly the non-
condition I discovered) at xmin?

I did not find any examples of how to do this and it does not seem to be 
straightforward. Do I need to convert from f, f', f'' to f, g, g' with g=f' to 
change the f'(xmax) condition to a Dirichlet one for g? But that does not seem 
to be feasible since I can not think of what equation g (or f') should obey in 
the interior - recall that I just have a single equation, F(f, f', f'') = 0.

Cheers,
-Juha

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