Date: 2022-08-09T09:05:21+00:00

Actual source code: dmerg2.c
slepc-3.17.2 2022-08-09
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      1: /*
      2:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      3:    SLEPc - Scalable Library for Eigenvalue Problem Computations
      4:    Copyright (c) 2002-, Universitat Politecnica de Valencia, Spain

      6:    This file is part of SLEPc.
      7:    SLEPc is distributed under a 2-clause BSD license (see LICENSE).
      8:    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
      9: */
     10: /*
     11:    BDC - Block-divide and conquer (see description in README file)
     12: */

     14: #include <slepc/private/dsimpl.h>
     15: #include <slepcblaslapack.h>

     17: PetscErrorCode BDC_dmerg2_(const char *jobz,PetscBLASInt rkct,PetscBLASInt n,
     18:         PetscReal *ev,PetscReal *q,PetscBLASInt ldq,PetscBLASInt *indxq,
     19:         PetscReal *rho,PetscReal *u,PetscBLASInt sbrkp1,PetscReal *v,
     20:         PetscBLASInt sbrk,PetscBLASInt cutpnt,PetscReal *work,PetscBLASInt lwork,
     21:         PetscBLASInt *iwork,PetscReal tol,PetscBLASInt *info,PetscBLASInt jobz_len)
     22: {
     23: /*  -- Routine written in LAPACK Version 3.0 style -- */
     24: /* *************************************************** */
     25: /*     Written by */
     26: /*     Michael Moldaschl and Wilfried Gansterer */
     27: /*     University of Vienna */
     28: /*     last modification: March 16, 2014 */

     30: /*     Small adaptations of original code written by */
     31: /*     Wilfried Gansterer and Bob Ward, */
     32: /*     Department of Computer Science, University of Tennessee */
     33: /*     see https://doi.org/10.1137/S1064827501399432 */
     34: /* *************************************************** */

     36: /*  Purpose */
     37: /*  ======= */

     39: /*  DMERG2 computes the updated eigensystem of a diagonal matrix after */
     40: /*  modification by a rank-one symmetric matrix.  The diagonal matrix */
     41: /*  consists of two diagonal submatrices, and the vectors defining the */
     42: /*  rank-1 matrix similarly have two underlying subvectors each. */
     43: /*  The dimension of the first subproblem is CUTPNT, the dimension of */
     44: /*  the second subproblem is N-CUTPNT. */

     46: /*  T = Q(in) (EV(in) + RHO * Z*Z') Q'(in) = Q(out) * EV(out) * Q'(out) */

     48: /*     where Z = Q'[V U']', where V is a row vector and U is a column */
     49: /*     vector with dimensions corresponding to the two underlying */
     50: /*     subproblems. */

     52: /*     The eigenvectors of the original matrix are stored in Q, and the */
     53: /*     eigenvalues in EV.  The algorithm consists of three stages: */

     55: /*        The first stage consists of deflating the size of the problem */
     56: /*        when there are multiple eigenvalues or if there is a zero in */
     57: /*        the Z vector.  For each such occurrence the dimension of the */
     58: /*        secular equation problem is reduced by one.  This stage is */
     59: /*        performed by the routine DSRTDF. */

     61: /*        The second stage consists of calculating the updated */
     62: /*        eigenvalues. This is done by finding the roots of the secular */
     63: /*        equation via the routine DLAED4 (as called by DLAED3M). */
     64: /*        This routine also calculates the eigenvectors of the current */
     65: /*        problem. */

     67: /*        If(JOBZ.EQ.'D') then the final stage consists */
     68: /*        of computing the updated eigenvectors directly using the updated */
     69: /*        eigenvalues. The eigenvectors for the current problem are multiplied */
     70: /*        with the eigenvectors from the overall problem. */

     72: /*  Arguments */
     73: /*  ========= */

     75: /*  JOBZ   (input) CHARACTER*1 */
     76: /*          = 'N': Compute eigenvalues only (not implemented); */
     77: /*          = 'D': Compute eigenvalues and eigenvectors. */
     78: /*                 Eigenvectors are accumulated in the divide-and-conquer */
     79: /*                 process. */

     81: /*  RKCT   (input) INTEGER */
     82: /*         The number of the rank modification which is accounted for */
     83: /*         (RKCT >= 1). Required parameter, because the update operation of the */
     84: /*         modification vector can be performed much more efficiently */
     85: /*         if RKCT.EQ.1. In that case, the eigenvector matrix is still */
     86: /*         block-diagonal. For RKCT.GE.2 the eigenvector matrix for the update */
     87: /*         operation has filled up and is a full matrix. */

     89: /*  N      (input) INTEGER */
     90: /*         The dimension of the symmetric block tridiagonal matrix. */
     91: /*         N >= 0. */

     93: /*  EV     (input/output) DOUBLE PRECISION array, dimension (N) */
     94: /*         On entry, the eigenvalues (=diagonal values) of the */
     95: /*         rank-1-perturbed matrix. */
     96: /*         On exit, the eigenvalues of the repaired matrix. */

     98: /*  Q      (input/output) DOUBLE PRECISION array, dimension (LDQ,N) */
     99: /*         On entry, the eigenvectors of the rank-1-perturbed matrix. */
    100: /*         On exit, the eigenvectors of the repaired tridiagonal matrix. */

    102: /*  LDQ    (input) INTEGER */
    103: /*         The leading dimension of the array Q.  LDQ >= max(1,N). */

    105: /*  INDXQ  (input/output) INTEGER array, dimension (N) */
    106: /*         On entry, the permutation which separately sorts the two */
    107: /*         subproblems in EV into ascending order. */
    108: /*         On exit, the permutation which will reintegrate the */
    109: /*         subproblems back into sorted order, */
    110: /*         i.e. EV(INDXQ(I = 1, N)) will be in ascending order. */

    112: /*  RHO    (input/output) DOUBLE PRECISION */
    113: /*         The scalar in the rank-1 perturbation. Modified (multiplied */
    114: /*         by 2) in DSRTDF. */

    116: /*  U      (input) DOUBLE PRECISION array; dimension (SBRKP1), where SBRKP1 */
    117: /*         is the size of the first (original) block after CUTPNT. */
    118: /*         The column vector of the rank-1 subdiagonal connecting the */
    119: /*         two diagonal subproblems. */
    120: /*         Theoretically, zero entries might have to be appended after U */
    121: /*         in order to make it have dimension (N-CUTPNT). However, this */
    122: /*         is not required because it can be accounted for in the */
    123: /*         matrix-vector product using the argument SBRKP1. */

    125: /*  SBRKP1 (input) INTEGER */
    126: /*         Dimension of the relevant (non-zero) part of the vector U. */
    127: /*         Equal to the size of the first original block after the */
    128: /*         breakpoint. */

    130: /*  V      (input) DOUBLE PRECISION array; dimension (SBRK), where SBRK */
    131: /*         is the size of the last (original) block before CUTPNT. */
    132: /*         The row vector of the rank-1 subdiagonal connecting the two */
    133: /*         diagonal subproblems. */
    134: /*         Theoretically, zero entries might have to be inserted in front */
    135: /*         of V in order to make it have dimension (CUTPNT). However, this */
    136: /*         is not required because it can be accounted for in the */
    137: /*         matrix-vector product using the argument SBRK. */

    139: /*  SBRK   (input) INTEGER */
    140: /*         Dimension of the relevant (non-zero) part of the vector V. */
    141: /*         Equal to the size of the last original block before the */
    142: /*         breakpoint. */

    144: /*  CUTPNT (input) INTEGER */
    145: /*         The location of the last eigenvalue of the leading diagonal */
    146: /*         block.  min(1,N) <= CUTPNT <= max(1,N). */

    148: /*  WORK   (workspace) DOUBLE PRECISION array, dimension (LWORK) */

    150: /*  LWORK  (input) INTEGER */
    151: /*         The dimension of the array WORK. */
    152: /*         In order to guarantee correct results in all cases, */
    153: /*         LWORK must be at least (2*N**2 + 3*N). In many cases, */
    154: /*         less workspace is required. The absolute minimum required is */
    155: /*         (N**2 + 3*N). */
    156: /*         If the workspace provided is not sufficient, the routine will */
    157: /*         return a corresponding error code and report how much workspace */
    158: /*         was missing (see INFO). */
    159: /*         NOTE: This parameter is needed for determining whether enough */
    160: /*               workspace is provided, and, if not, for computing how */
    161: /*               much workspace is needed. */

    163: /*  IWORK  (workspace) INTEGER array, dimension (4*N) */

    165: /*  TOL    (input) DOUBLE PRECISION */
    166: /*         User specified deflation tolerance for the routine DSRTDF. */

    168: /*  INFO   (output) INTEGER */
    169: /*          = 0:  successful exit. */
    170: /*          < -200: not enough workspace */
    171: /*                ABS(INFO + 200) numbers have to be stored in addition */
    172: /*                to the workspace provided, otherwise some eigenvectors */
    173: /*                will be incorrect. */
    174: /*          < 0, > -99:  if INFO.EQ.-i, the i-th argument had an */
    175: /*                       illegal value. */
    176: /*          > 0:  if INFO.EQ.1, an eigenvalue did not converge */
    177: /*                if INFO.EQ.2, the deflation counters DZ and DE do not sum */
    178: /*                              up to the total number N-K of components */
    179: /*                              deflated */

    181: /*  Further Details */
    182: /*  =============== */

    184: /*  Based on code written by */
    185: /*     Wilfried Gansterer and Bob Ward, */
    186: /*     Department of Computer Science, University of Tennessee */

    188: /*  Based on the design of the LAPACK code Dlaed1.f written by Jeff */
    189: /*  Rutter, Computer Science Division, University of California at */
    190: /*  Berkeley, and modified by Francoise Tisseur, University of Tennessee. */

    192: /*  ===================================================================== */

    194:   PetscBLASInt   i, k, n1, n2, de, is, dz, iw, iz, iq2, nmc, cpp1;
    195:   PetscBLASInt   indx, indxc, indxp, lwmin, idlmda;
    196:   PetscBLASInt   spneed, coltyp, tmpcut, i__1, i__2, one=1, mone=-1;
    197:   char           defl[1];
    198:   PetscReal      done = 1.0, dzero = 0.0;

    200:   *info = 0;
    201:   lwmin = n*n + n * 3;

    203:   if (n < 0) *info = -3;
    204:   else if (ldq < PetscMax(1,n)) *info = -6;
    205:   else if (cutpnt < PetscMin(1,n) || cutpnt > PetscMax(1,n)) *info = -13;
    206:   else if (lwork < lwmin) *info = -15;

    209: /* **************************************************************************** */

    211:   /* Quick return if possible */

    213:   if (n == 0) PetscFunctionReturn(0);

    215: /* **************************************************************************** */

    217:   /* The following values are integer pointers which indicate */
    218:   /* the portion of the workspace used by a particular array in DSRTDF */
    219:   /* and DLAED3M. */

    221:   iz = 0;
    222:   idlmda = iz + n;
    223:   iw = idlmda + n;
    224:   iq2 = iw + n;
    225:   is = iq2 + n * n;

    227:   /* After the pointer IS the matrix S is stored and read in WORK */
    228:   /* in the routine DLAED3M. */

    230:   indx = 0;
    231:   indxc = indx + n;
    232:   coltyp = indxc + n;
    233:   indxp = coltyp + n;

    235:   /* If eigenvectors are to be accumulated in the divide-and-conquer */
    236:   /* process (JOBZ.EQ.'D') form the z-vector which consists of */
    237:   /* Q_1^T * V and Q_2^T * U. */

    239:   cpp1 = cutpnt + 1;
    240:   if (rkct == 1) {

    242:     /* for the first rank modification the eigenvector matrix has */
    243:     /* special block-diagonal structure and therefore Q_1^T * V and */
    244:     /* Q_2^T * U can be formed separately. */

    246:     PetscStackCallBLAS("BLASgemv",BLASgemv_("T", &sbrk, &cutpnt, &done,
    247:               &q[cutpnt - sbrk], &ldq, v, &one, &dzero, &work[iz], &one));
    248:     nmc = n - cutpnt;
    249:     PetscStackCallBLAS("BLASgemv",BLASgemv_("T", &sbrkp1, &nmc, &done,
    250:               &q[cpp1-1 + (cpp1-1)*ldq], &ldq, u,
    251:               &one, &dzero, &work[iz + cutpnt], &one));

    253:   } else {

    255:     /* for the higher rank modifications, the vectors V and U */
    256:     /* have to be multiplied with the full eigenvector matrix */

    258:     PetscStackCallBLAS("BLASgemv",BLASgemv_("T", &sbrk, &n, &done,
    259:               &q[cutpnt - sbrk], &ldq, v, &one, &dzero, &work[iz], &one));
    260:     PetscStackCallBLAS("BLASgemv",BLASgemv_("T", &sbrkp1, &n, &done, &q[cpp1-1],
    261:               &ldq, u, &one, &done, &work[iz], &one));

    263:   }

    265: /* **************************************************************************** */

    267:   /* Deflate eigenvalues. */

    269:   if (rkct == 1) {

    271:     /* for the first rank modification we need the actual cutpoint */

    273:     n1 = cutpnt;
    274:     tmpcut = cutpnt;
    275:   } else {

    277:     /* for the later rank modifications there is no actual cutpoint any more */

    279:     n1 = n;

    281:     /* The original value of CUTPNT has to be preserved for the next time */
    282:     /* this subroutine is called (therefore, CUTPNT is an INPUT parameter */
    283:     /* and not to be changed). Thus, assign N to TMPCUT and use the local */
    284:     /* variable TMPCUT from now on for the cut point. */

    286:     tmpcut = n;
    287:   }

    289:   /* initialize the flag DEFL (indicates whether deflation occurred - */
    290:   /* this information is needed later in DLAED3M) */

    292:   *(unsigned char *)defl = '0';

    294:   /* call DSRTDF for deflation */

    296:   PetscCall(BDC_dsrtdf_(&k, n, n1, ev, q, ldq, indxq, rho, &work[iz],
    297:           &work[idlmda], &work[iw], &work[iq2], &iwork[indx],
    298:           &iwork[indxc], &iwork[indxp], &iwork[coltyp], tol, &dz, &de, info));

    301:   if (k < n) {

    303:    /* ....some deflation occurred in dsrtdf, set the flag DEFL */
    304:    /*     (needed in DLAED3M.f, since Givens rotations need to be */
    305:    /*     applied to the eigenvector matrix only if some deflation */
    306:    /*     happened) */

    308:     *(unsigned char *)defl = '1';
    309:   }

    311: /* **************************************************************************** */

    313:   /* Solve the Secular Equation. */

    315:   if (k != 0) {

    317:     /* ....not everything was deflated. */

    319:     /* ....check whether enough workspace is available: */

    321:     /* Note that the following (upper) bound SPNEED for the workspace */
    322:     /* requirements should also hold in the extreme case TMPCUT=N, */
    323:     /* which happens for every rank modification after the first one. */

    325:     i__1 = (iwork[coltyp] + iwork[coltyp+1]) * k;
    326:     i__2 = (iwork[coltyp+1] + iwork[coltyp + 2]) * k;
    327:     spneed = is + PetscMax(i__1,i__2) - 1;

    331:     /* calling DLAED3M for solving the secular equation. */

    333:     PetscCall(BDC_dlaed3m_(jobz, defl, k, n, tmpcut, ev, q, ldq,
    334:                 *rho, &work[idlmda], &work[iq2], &iwork[indxc], &iwork[coltyp],
    335:                 &work[iw], &work[is], info, 1, 1));

    338:     /* Prepare the INDXQ sorting permutation. */

    340:     n1 = k;
    341:     n2 = n - k;
    342:     PetscStackCallBLAS("LAPACKlamrg",LAPACKlamrg_(&n1, &n2, ev, &one, &mone, indxq));
    343:     if (k == 0) for (i = 0; i < n; ++i) indxq[i] = i+1;

    345:   } else {

    347:     /* ....everything was deflated (K.EQ.0) */

    349:     for (i = 0; i < n; ++i) indxq[i] = i+1;
    350:   }
    351:   PetscFunctionReturn(0);
    352: }