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.

See Also

KSP: Linear System Solvers, KSP, KSPSolve(), KSPMonitor()

Level

developer

Location

src/ksp/ksp/interface/itres.c

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Index of all KSP routines
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Index of all manual pages