Conjugate Gradient technique

Barry Smith bsmith at
Thu May 14 16:03:41 CDT 2009

    Please take a look at the manual pages for MATSHELL and  
MatShellCreate(). You will need to create a matrix with  
MatCreateShell() and then
supply your matrix vector operation with MatShellSetOperation() A  
fortran example can be found at


On May 14, 2009, at 3:58 PM, Barai, Pallab wrote:

> Hello,
> I am using PETSc to solve a set of linear equations "Sx=b".
> Here "b" is known and "x" is the trial solution.
> The complete (assembled) form of S is not known. That is why I am  
> not able to use something like "KSPSolve".
> But given a trial solution "x", I can calculate "S*x" using a  
> "MatVec" routine.
> Is it possible to use the Conjugate Gradient (CG) technique to find  
> a solution in this case? In place of "S", I can give "S*x" as the  
> input.
> It will be great if someone can show me some direction. If this  
> thing has already been discussed before, the link to that thread  
> will be sufficient.
> Thanking you.
> Pallab Barai

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