KSPInitialResidual#

Computes the residual. Either b - ACu = b - Ax with right preconditioning or C(b - A*x) with left preconditioning; the latter residual is often called the “preconditioned residual”.

Synopsis#

#include "petscksp.h" 
PetscErrorCode KSPInitialResidual(KSP ksp, Vec vsoln, Vec vt1, Vec vt2, Vec vres, Vec vb)

Collective

Input Parameters#

ksp - the KSP solver object
vsoln - solution to use in computing residual
vt1 - temporary work vector
vt2 - temporary work vector
vb - right-hand-side vector

Output Parameter#

vres - calculated residual

Note#

This routine assumes that an iterative method, designed for \( A x = b \) will be used with a preconditioner, C, such that the actual problem is either

  AC u = b (right preconditioning) or
  CA x = Cb (left preconditioning).

This means that the calculated residual will be scaled and/or preconditioned; the true residual \( b-Ax \) is returned in the vt2 temporary work vector.

Level#

developer

Location#

src/ksp/ksp/interface/itres.c

Index of all KSP routines
Table of Contents for all manual pages
Index of all manual pages