[petsc-users] (no subject)

[Li Luo]

Dear Developers,

I tried to use the multi-color finite-difference (MC-FD) method for
constructing the Jacobians. However, I find it is very slow compared to the
exact Jacobian.
My implementation of MC-FD Jacobian is posted below, would you please check
whether I am correct? Anything missed? Thank you!

////////// Setup phase:
          MatStructure flag;
          ISColoring   iscoloring;
          ierr = MatGetColoring(Jac,MATCOLORINGSL,&iscoloring);
          ierr = MatFDColoringCreate(Jac,iscoloring,&this->matfdcoloring);
          ierr =
MatFDColoringSetFunction(this->matfdcoloring,(PetscErrorCode
(*)(void))__libmesh_petsc_snes_residual,(void *)this);
          ierr = MatFDColoringSetFromOptions(this->matfdcoloring);
          ierr = ISColoringDestroy(&iscoloring);

//////////// Apply:
          ierr = MatZeroEntries(*jac);CHKERRQ(ierr);
          ierr =
MatFDColoringApply(*jac,solver->matfdcoloring,x,msflag,snes);

Best regards,
Li Luo

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