Hi, I am not sure that I understand the MatStructure flag in the call of KSPSetOperators correctly. If I use KSPSetOperators(ksp, A, P, DIFFERENT_NONZERO_PATTERN) and then solve two linear systems with the same matrix operators but different rhs is the preconditioner reassembled in every solve. I.e., if I call KSPSolve(ksp,b1,x1); KSPSolve(ksp,b2,x2); And if I use KSPSetOperators(ksp, A, P, SAME_PRECONDITIONER) the preconditioner is only setup one time and reused later. Or is the flag only important if I change the matrix operators in between. Thank you, Verena ________________________________ This e-mail message (including any attachments) is for the sole use of the intended recipient(s) and may contain confidential and privileged information. If the reader of this message is not the intended recipient, you are hereby notified that any dissemination, distribution or copying of this message (including any attachments) is strictly prohibited. If you have received this message in error, please contact the sender by reply e-mail message and destroy all copies of the original message (including attachments).