1: /*
  2:    Functions in this file reorder the Ritz values in the (modified) Leja order.
  3: */
  4: #include <../src/ksp/ksp/impls/gmres/agmres/agmresimpl.h>

  6: static PetscErrorCode KSPAGMRESLejafmaxarray(PetscScalar *re, PetscInt pt, PetscInt n, PetscInt *pos)
  7: {
  8:   PetscInt    i;
  9:   PetscScalar mx;

 11:   PetscFunctionBegin;
 12:   mx   = re[0];
 13:   *pos = 0;
 14:   for (i = pt; i < n; i++) {
 15:     if (mx < re[i]) {
 16:       mx   = re[i];
 17:       *pos = i;
 18:     }
 19:   }
 20:   PetscFunctionReturn(PETSC_SUCCESS);
 21: }

 23: static PetscErrorCode KSPAGMRESLejaCfpdMax(PetscScalar *rm, PetscScalar *im, PetscInt *spos, PetscInt nbre, PetscInt n, PetscInt *rpos)
 24: {
 25:   PetscScalar rd, id, pd, max;
 26:   PetscInt    i, j;

 28:   PetscFunctionBegin;
 29:   pd    = 1.0;
 30:   max   = 0.0;
 31:   *rpos = 0;
 32:   for (i = 0; i < n; i++) {
 33:     for (j = 0; j < nbre; j++) {
 34:       rd = rm[i] - rm[spos[j]];
 35:       id = im[i] - im[spos[j]];
 36:       pd = pd * PetscSqrtReal(rd * rd + id * id);
 37:     }
 38:     if (max < pd) {
 39:       *rpos = i;
 40:       max   = pd;
 41:     }
 42:     pd = 1.0;
 43:   }
 44:   PetscFunctionReturn(PETSC_SUCCESS);
 45: }

 47: PetscErrorCode KSPAGMRESLejaOrdering(PetscScalar *re, PetscScalar *im, PetscScalar *rre, PetscScalar *rim, PetscInt m)
 48: {
 49:   PetscInt    *spos;
 50:   PetscScalar *n_cmpl, temp;
 51:   PetscInt     i, pos, j;

 53:   PetscFunctionBegin;
 54:   PetscCall(PetscMalloc1(m, &n_cmpl));
 55:   PetscCall(PetscMalloc1(m, &spos));
 56:   /* Check the proper order of complex conjugate pairs */
 57:   j = 0;
 58:   while (j < m) {
 59:     if (im[j] != 0.0) {  /* complex eigenvalue */
 60:       if (im[j] < 0.0) { /* change the order */
 61:         temp      = im[j + 1];
 62:         im[j + 1] = im[j];
 63:         im[j]     = temp;
 64:       }
 65:       j += 2;
 66:     } else j++;
 67:   }

 69:   for (i = 0; i < m; i++) n_cmpl[i] = PetscSqrtReal(re[i] * re[i] + im[i] * im[i]);
 70:   PetscCall(KSPAGMRESLejafmaxarray(n_cmpl, 0, m, &pos));
 71:   j = 0;
 72:   if (im[pos] >= 0.0) {
 73:     rre[0] = re[pos];
 74:     rim[0] = im[pos];
 75:     j++;
 76:     spos[0] = pos;
 77:   }
 78:   while (j < (m)) {
 79:     if (im[pos] > 0) {
 80:       rre[j]  = re[pos + 1];
 81:       rim[j]  = im[pos + 1];
 82:       spos[j] = pos + 1;
 83:       j++;
 84:     }
 85:     PetscCall(KSPAGMRESLejaCfpdMax(re, im, spos, j, m, &pos));
 86:     if (im[pos] < 0) pos--;

 88:     if ((im[pos] >= 0) && (j < m)) {
 89:       rre[j]  = re[pos];
 90:       rim[j]  = im[pos];
 91:       spos[j] = pos;
 92:       j++;
 93:     }
 94:   }
 95:   PetscCall(PetscFree(spos));
 96:   PetscCall(PetscFree(n_cmpl));
 97:   PetscFunctionReturn(PETSC_SUCCESS);
 98: }