petsc-3.7.7 2017-09-25

KSPInitialResidual

Computes the residual. Either b - A*C*u = b - A*x with right preconditioning or C*(b - A*x) with left preconditioning; that later 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.

Keywords