[petsc-users] PETSC for singular system

[Yaxiong Chen via petsc-users]

Hello,


I am trying to use PETSC to solve a singular system like the following.

[cid:ef7b4672-623e-48d7-b9fa-6e8d4ed67b5f].

This equals inserting rows and columns at arbitrary place(Actually I even don't 
know whether it is singular or not. Sometimes some degree of freedom x_i may 
not participate in the global matrix)

[cid:0c347c3e-462d-4fe8-9718-273339c2c1f2]

I searched some discussion online and tried to remove the nullspace with the 
following code:

     call KSPCreate(PETSC_COMM_WORLD,ksp,ierr)
     call KSPSetOperators(ksp,Amat,Amat,ierr)
     call KSPSetFromOptions(ksp,ierr)
     call KSPSetType(ksp, KSPCG,ierr)
     call MatNullSpaceCreate( PETSC_COMM_WORLD, PETSC_TRUE, 0, dummyVecs, 
nullspace, ierr)
     call MatSetNullSpace(Amat,nullspace,ierr)
     call MatNullSpaceDestroy(nullspace,ierr)
     call KSPSolve(ksp,bvec,xvec,ierr)

But it still gives me some error saying Zero pivot in LU factorization.
I am just wondering how MatSetNullSpace() can handle this?

Thanks


Yaxiong Chen,

School of Mechanical Engineering, 3171

585 Purdue Mall

West Lafayette, IN 47907