PETSc version 3.15.5
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