Actual source code: itres.c

  1: #define PETSCKSP_DLL

 3:  #include include/private/kspimpl.h

  7: /*@C
  8:    KSPInitialResidual - Computes the residual. Either b - A*C*x with right
  9:      preconditioning or C*b - C*A*x with left preconditioning; that later
 10:      residual is often called the "preconditioned residual".

 12:    Collective on KSP

 14:    Input Parameters:
 15: +  vsoln    - solution to use in computing residual
 16: .  vt1, vt2 - temporary work vectors
 17: -  vb       - right-hand-side vector

 19:    Output Parameters:
 20: .  vres     - calculated residual

 22:    Notes:
 23:    This routine assumes that an iterative method, designed for
 24: $     A x = b
 25:    will be used with a preconditioner, C, such that the actual problem is either
 26: $     AC u = b (right preconditioning) or
 27: $     CA x = Cb (left preconditioning).
 28:    This means that the calculated residual will be scaled and/or preconditioned;
 29:    the true residual
 30: $     b-Ax
 31:    is returned in the vt2 temporary.

 33:    Level: developer

 35: .keywords: KSP, residual

 37: .seealso:  KSPMonitor()
 38: @*/
 39: PetscErrorCode  KSPInitialResidual(KSP ksp,Vec vsoln,Vec vt1,Vec vt2,Vec vres,Vec vb)
 40: {
 41:   MatStructure   pflag;
 42:   Mat            Amat,Pmat;

 50:   PCGetOperators(ksp->pc,&Amat,&Pmat,&pflag);
 51:   if (!ksp->guess_zero) {
 52:     /* skip right scaling since current guess already has it */
 53:     KSP_MatMult(ksp,Amat,vsoln,vt1);
 54:     VecCopy(vb,vt2);
 55:     VecAXPY(vt2,-1.0,vt1);
 56:     (ksp->pc_side == PC_RIGHT)?(VecCopy(vt2,vres)):(KSP_PCApply(ksp,vt2,vres));
 57:     PCDiagonalScaleLeft(ksp->pc,vres,vres);
 58:   } else {
 59:     VecCopy(vb,vt2);
 60:     if (ksp->pc_side == PC_RIGHT) {
 61:       PCDiagonalScaleLeft(ksp->pc,vb,vres);
 62:     } else if (ksp->pc_side == PC_LEFT) {
 63:       KSP_PCApply(ksp,vb,vres);
 64:       PCDiagonalScaleLeft(ksp->pc,vres,vres);
 65:     } else if (ksp->pc_side == PC_SYMMETRIC) {
 66:       PCApplySymmetricLeft(ksp->pc, vb, vres);
 67:     } else {
 68:       SETERRQ1(PETSC_ERR_SUP, "Invalid preconditioning side %d", (int)ksp->pc_side);
 69:     }
 70:   }
 71:   return(0);
 72: }

 76: /*@
 77:    KSPUnwindPreconditioner - Unwinds the preconditioning in the solution. That is,
 78:      takes solution to the preconditioned problem and gets the solution to the 
 79:      original problem from it.

 81:    Collective on KSP

 83:    Input Parameters:
 84: +  ksp  - iterative context
 85: .  vsoln - solution vector 
 86: -  vt1   - temporary work vector

 88:    Output Parameter:
 89: .  vsoln - contains solution on output  

 91:    Notes:
 92:    If preconditioning either symmetrically or on the right, this routine solves 
 93:    for the correction to the unpreconditioned problem.  If preconditioning on 
 94:    the left, nothing is done.

 96:    Level: advanced

 98: .keywords: KSP, unwind, preconditioner

100: .seealso: KSPSetPreconditionerSide()
101: @*/
102: PetscErrorCode  KSPUnwindPreconditioner(KSP ksp,Vec vsoln,Vec vt1)
103: {

109:   if (ksp->pc_side == PC_RIGHT) {
110:     KSP_PCApply(ksp,vsoln,vt1);
111:     PCDiagonalScaleRight(ksp->pc,vt1,vsoln);
112:   } else if (ksp->pc_side == PC_SYMMETRIC) {
113:     PCApplySymmetricRight(ksp->pc,vsoln,vt1);
114:     VecCopy(vt1,vsoln);
115:   } else {
116:     PCDiagonalScaleRight(ksp->pc,vsoln,vsoln);
117:   }
118:   return(0);
119: }