Re: [petsc-users] Fwd: Implementing a homotopy solver

[Smith, Barry F.]

> On Jul 22, 2018, at 4:31 PM, zakaryah <zakar...@gmail.com> wrote:
> 
> OK, thanks, I understand now.
> 
> FormJacobian() has two matrices as arguments, the Jacobian Amat and the 
> preconditioner Pmat, which may be the same.  My FormJacobian() routine sets 
> the values of the Jacobian in Pmat.  So, to calculate the effective nullspace 
> of the submatrix,

          What "submatrix" are you referring to?  Are you calling Pmat a 
submatrix?, if so why?

          Is b then here the zero vector?


> I want to solve Pmat u = b.  To do this within FormJacobian(), can I assemble 
> Pmat, call SNESGetKSP(snes,&ksp), and then KSPSolve(ksp,b,u)?  Is it safe to 
> assume that the KSP matrix is Pmat?
> 
> 

    The KSPSolve used by SNES solves    Amat delta u = -F(u)  building the 
preconditioner from the matrix Pmat.  


>