Actual source code: itres.c

```  1: #include <petsc/private/kspimpl.h>

3: /*@
4:   KSPInitialResidual - Computes the residual. Either b - A*C*u = b - A*x with right
5:   preconditioning or C*(b - A*x) with left preconditioning; the latter
6:   residual is often called the "preconditioned residual".

8:   Collective

10:   Input Parameters:
11: + ksp   - the `KSP` solver object
12: . vsoln - solution to use in computing residual
13: . vt1   - temporary work vector
14: . vt2   - temporary work vector
15: - vb    - right-hand-side vector

17:   Output Parameter:
18: . vres - calculated residual

20:   Level: developer

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

33: .seealso: [](ch_ksp), `KSP`, `KSPSolve()`, `KSPMonitor()`
34: @*/
35: PetscErrorCode KSPInitialResidual(KSP ksp, Vec vsoln, Vec vt1, Vec vt2, Vec vres, Vec vb)
36: {
37:   Mat Amat, Pmat;

39:   PetscFunctionBegin;
44:   if (!ksp->pc) PetscCall(KSPGetPC(ksp, &ksp->pc));
45:   PetscCall(PCGetOperators(ksp->pc, &Amat, &Pmat));
46:   if (!ksp->guess_zero) {
47:     /* skip right scaling since current guess already has it */
48:     PetscCall(KSP_MatMult(ksp, Amat, vsoln, vt1));
49:     PetscCall(VecCopy(vb, vt2));
50:     PetscCall(VecAXPY(vt2, -1.0, vt1));
51:     if (ksp->pc_side == PC_RIGHT) {
52:       PetscCall(PCDiagonalScaleLeft(ksp->pc, vt2, vres));
53:     } else if (ksp->pc_side == PC_LEFT) {
54:       PetscCall(KSP_PCApply(ksp, vt2, vres));
55:       PetscCall(PCDiagonalScaleLeft(ksp->pc, vres, vres));
56:     } else if (ksp->pc_side == PC_SYMMETRIC) {
57:       PetscCall(PCApplySymmetricLeft(ksp->pc, vt2, vres));
58:     } else SETERRQ(PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "Invalid preconditioning side %d", (int)ksp->pc_side);
59:   } else {
60:     PetscCall(VecCopy(vb, vt2));
61:     if (ksp->pc_side == PC_RIGHT) {
62:       PetscCall(PCDiagonalScaleLeft(ksp->pc, vb, vres));
63:     } else if (ksp->pc_side == PC_LEFT) {
64:       PetscCall(KSP_PCApply(ksp, vb, vres));
65:       PetscCall(PCDiagonalScaleLeft(ksp->pc, vres, vres));
66:     } else if (ksp->pc_side == PC_SYMMETRIC) {
67:       PetscCall(PCApplySymmetricLeft(ksp->pc, vb, vres));
68:     } else SETERRQ(PetscObjectComm((PetscObject)ksp), PETSC_ERR_SUP, "Invalid preconditioning side %d", (int)ksp->pc_side);
69:   }
70:   /* This may be true only on a subset of MPI ranks; setting it here so it will be detected by the first norm computation in the Krylov method */
71:   if (ksp->reason == KSP_DIVERGED_PC_FAILED) PetscCall(VecSetInf(vres));
72:   PetscFunctionReturn(PETSC_SUCCESS);
73: }

75: /*@
76:   KSPUnwindPreconditioner - Unwinds the preconditioning in the solution. That is,
77:   takes solution to the preconditioned problem and gets the solution to the
78:   original problem from it.

80:   Collective

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

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

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

97: .seealso: [](ch_ksp), `KSP`, `KSPSetPCSide()`
98: @*/
99: PetscErrorCode KSPUnwindPreconditioner(KSP ksp, Vec vsoln, Vec vt1)
100: {
101:   PetscFunctionBegin;
104:   if (!ksp->pc) PetscCall(KSPGetPC(ksp, &ksp->pc));
105:   if (ksp->pc_side == PC_RIGHT) {
106:     PetscCall(KSP_PCApply(ksp, vsoln, vt1));
107:     PetscCall(PCDiagonalScaleRight(ksp->pc, vt1, vsoln));
108:   } else if (ksp->pc_side == PC_SYMMETRIC) {
109:     PetscCall(PCApplySymmetricRight(ksp->pc, vsoln, vt1));
110:     PetscCall(VecCopy(vt1, vsoln));
111:   } else {
112:     PetscCall(PCDiagonalScaleRight(ksp->pc, vsoln, vsoln));
113:   }
114:   PetscFunctionReturn(PETSC_SUCCESS);
115: }
```