petsc-3.14.6 2021-03-30
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KSPInitialResidual

 Computes the residual. Either b - A*C*u = b - A*x 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 on ksp

Input Parameters

vsoln - solution to use in computing residual
vt1, vt2 - temporary work vectors
vb - right-hand-side vector

Output Parameters

vres - calculated residual

Notes

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.

See Also

KSPMonitor()

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