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November 2025

25 participants
22 discussions

norm of KSPBuildResidual does not match norm computed from KSPBuildSolution
by Moral Sanchez, Elena 04 Nov '25

04 Nov '25

Hi, I am running CG with a Jacobi preconditioner. I have a monitor function that prints the residual and saves the solution at every iteration. To get the solution at every iteration, I am using the function KSPBuildSolution. I am setting the KSP norm as UNPRECONDITIONED. The convergence test is consistent with the 2-norm of KSPBuildResidual. However this norm does not match the 2-norm of the residual computed explicitly from the solution (obtained with KSPBuildSolution). It also does not match the preconditioned norm. What norm is it computing? When the CG is not preconditioned, the norm of KSPBuildResidual and the norm of the residual computed from the solution match, as I expected. This is KSPView(): KSP Object: 1 MPI process type: cg variant HERMITIAN maximum iterations=100, nonzero initial guess tolerances: relative=1e-08, absolute=1e-08, divergence=10000. left preconditioning using UNPRECONDITIONED norm type for convergence test PC Object: 1 MPI process type: jacobi type DIAGONAL linear system matrix = precond matrix: Mat Object: 1 MPI process type: nest rows=524, cols=524 Matrix object: type=nest, rows=3, cols=3 MatNest structure: (0,0) : type=mpiaij, rows=176, cols=176 (0,1) : NULL (0,2) : NULL (1,0) : NULL (1,1) : type=mpiaij, rows=172, cols=172 (1,2) : NULL (2,0) : NULL (2,1) : NULL (2,2) : type=mpiaij, rows=176, cols=176 Cheers, Elena Moral Sánchez

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Segmentation violation in DMSwarmMigrate(sdm_, PETSC_TRUE)
by prateekgupta1709＠gmail.com 04 Nov '25

04 Nov '25

Hi, I am writing a basic particle tracking code with an existing periodic DMDA. All velocity calculations and position updates work fine but migration throws segfault. I have checked and particles are within the periodic box as well. I discovered that there is an internal field for coordinates which has to be defined using its identifier instead of explicitly registering a field. I am not registering any velocity field (using external vectors). Is there something I am missing? Thanks, Prateek

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