[petsc-users] problem with MatShellGetContext

[Nicolas Pozin]

Hello, 

I'm trying to solve a system with a matrix free operator and through conjugate gradient method. 
To make ideas clear, I set up the following simple example (I am using petsc-3.6) and I get this error message : 
" 
[0]PETSC ERROR: --------------------- Error Message ------------------------------------ 
[0]PETSC ERROR: Invalid argument! 
[0]PETSC ERROR: Wrong type of object: Parameter # 1! 
[0]PETSC ERROR: ------------------------------------------------------------------------ 
[0]PETSC ERROR: Petsc Release Version 3.4.3, Oct, 15, 2013 
[0]PETSC ERROR: See docs/changes/index.html for recent updates. 
[0]PETSC ERROR: See docs/faq.html for hints about trouble shooting. 
[0]PETSC ERROR: See docs/index.html for manual pages. 
[0]PETSC ERROR: ------------------------------------------------------------------------ 
[0]PETSC ERROR: ./test on a ubuntu_release named pl-59080 by npozin Wed Aug 5 10:55:26 2015 
[0]PETSC ERROR: Libraries linked from /home/npozin/Felisce_libraries/petsc_3.4.3/ubuntu_release/lib 
[0]PETSC ERROR: Configure run at Wed Jul 22 16:18:36 2015 
[0]PETSC ERROR: Configure options PETSC_ARCH=ubuntu_release --with-cxx=g++ --with-fc=gfortran --with-cc=gcc --with-x=0 --download-openmpi --download-f-blas-lapack --download-superlu --download-superlu_dist --with-superlu_dist=1 --download-metis --download-mumps --download-parmetis --with-superlu_dist=1 --download-boost --with-boost=1 --download-scalapack with-external-packages-dir=/home/npozin/Felisce_libraries/petsc_3.4.3/packages 
[0]PETSC ERROR: ------------------------------------------------------------------------ 
[0]PETSC ERROR: MatShellGetContext() line 202 in /home/npozin/Felisce_libraries/petsc_3.4.3/src/mat/impls/shell/shell.c 
End userMult 
[0]PETSC ERROR: MatMult() line 2179 in /home/npozin/Felisce_libraries/petsc_3.4.3/src/mat/interface/matrix.c 
[0]PETSC ERROR: KSP_MatMult() line 204 in /home/npozin/Felisce_libraries/petsc_3.4.3/include/petsc-private/kspimpl.h 
[0]PETSC ERROR: KSPSolve_CG() line 219 in /home/npozin/Felisce_libraries/petsc_3.4.3/src/ksp/ksp/impls/cg/cg.c 
[0]PETSC ERROR: KSPSolve() line 441 in /home/npozin/Felisce_libraries/petsc_3.4.3/src/ksp/ksp/interface/itfunc.c 
" 

I don't understand where the problem comes from with the matrix argument of MatShellGetContext. 
Any idea on what I do wrong? 

Thanks a lot, 
Nicolas 



#include <iostream> 
#include <petscksp.h> 

using namespace std; 


typedef struct { 
int val; 
} MyCtx; 


class ShellClass { 
Mat matShell; 
KSP ksp; 
PC pc; 
Vec x; 
Vec b; 

public: 
void userMult(Mat Amat, Vec x, Vec y) { 
cout << "Inside userMult" << endl; 

MyCtx *ctx; 
MatShellGetContext(Amat, (void *) ctx); 

cout << "End userMult" << endl; 
} 

void solveShell() { 
// context 
MyCtx *ctx = new MyCtx; 
ctx->val = 42; 

// pc 
PCCreate(PETSC_COMM_WORLD, &pc); 
PCSetType(pc, PCNONE); 

// ksp 
KSPCreate(PETSC_COMM_WORLD, &ksp); 
KSPSetType(ksp, KSPCG); 
KSPSetPC(ksp, pc); 
KSPSetFromOptions(ksp); 

// matshell 
int m = 10; 
int n = 10; 
MatCreateShell(PETSC_COMM_WORLD, m, n, PETSC_DETERMINE, PETSC_DETERMINE, ctx, &matShell); 
MatShellSetOperation(matShell, MATOP_MULT, (void(*)(void))&ShellClass::userMult); 


// create vectors 
MatCreateVecs(matShell, &x, 0); 
VecDuplicate(x, &b); 
VecSet(b, 1.); 

// set operators 
KSPSetOperators(ksp, matShell, matShell); 

// solve (call to userMult) 
KSPSolve(ksp, b, x); 
} 
}; 



int main(int argc, char** argv) { 
PetscInitialize(&argc, &argv, NULL, NULL); 

ShellClass foo; 
foo.solveShell(); 

PetscFinalize(); 
return 0; 
} 

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