Re: [petsc-users] Solving NON-Diagonally dominant sparse system

Kulkarni [kaushik...@gmail.com] Sent: Tuesday, April 11, 2017 7:07 AM To: Dave May Cc: PETSc users list Subject: Re: [petsc-users] Solving NON-Diagonally dominant sparse system But anyway since I am starting off with the exact solution itself, shouldn't the norm should be zero independent

Re: [petsc-users] Solving NON-Diagonally dominant sparse system

Nope - welcome to finite precision arithmetic. What's the condition number? On Tue, 11 Apr 2017 at 14:07, Kaushik Kulkarni wrote: > But anyway since I am starting off with the exact solution itself, > shouldn't the norm should be zero independent of the conditioning? > >

Re: [petsc-users] Solving NON-Diagonally dominant sparse system

But anyway since I am starting off with the exact solution itself, shouldn't the norm should be zero independent of the conditioning? On Tue, Apr 11, 2017 at 11:57 AM, Dave May wrote: > > > On Tue, 11 Apr 2017 at 07:28, Kaushik Kulkarni > wrote: >

Re: [petsc-users] Solving NON-Diagonally dominant sparse system

On Tue, 11 Apr 2017 at 07:28, Kaushik Kulkarni wrote: > A strange behavior I am observing is: > Problem: I have to solve A*x=rhs, and currently I am currently trying to > solve for a system where I know the exact solution. I have initialized the > exact solution in the Vec

Re: [petsc-users] Solving NON-Diagonally dominant sparse system

A strange behavior I am observing is: Problem: I have to solve A*x=rhs, and currently I am currently trying to solve for a system where I know the exact solution. I have initialized the exact solution in the Vec x_exact. MatMult(A, x_exact, dummy);// Storing the value of A*x_exact in dummy

Re: [petsc-users] Solving NON-Diagonally dominant sparse system

Thank you for the inputs. I tried Barry' s suggestion to use SuperLU, but the solution does not converge and on doing -ksp_monitor -ksp_converged_reason. I get the following error:- 240 KSP Residual norm 1.722571678777e+07 Linear solve did not converge due to DIVERGED_DTOL iterations 240 For some

Re: [petsc-users] Solving NON-Diagonally dominant sparse system

If you need to use SuperLU_DIST, the pivoting is done statically, using maximum weighted matching, so the small diagonals are usually taken care as well. It is not as good as partial pivoting, but works most of the time. Sherry On Mon, Apr 10, 2017 at 12:07 PM, Barry Smith

Re: [petsc-users] Solving NON-Diagonally dominant sparse system

I would suggest using ./configure --download-superlu and then when running the program -pc_type lu -pc_factor_mat_solver_package superlu Note that this is SuperLU, it is not SuperLU_DIST. Superlu uses partial pivoting for numerical stability so should be able to handle the small or zero