slaed7.c

#include "clapack.h"

/* Table of constant values */

static integer c__2 = 2;
static integer c__1 = 1;
static real c_b10 = 1.f;
static real c_b11 = 0.f;
static integer c_n1 = -1;

/* Subroutine */ int slaed7_(integer *icompq, integer *n, integer *qsiz, 
	integer *tlvls, integer *curlvl, integer *curpbm, real *d__, real *q, 
	integer *ldq, integer *indxq, real *rho, integer *cutpnt, real *
	qstore, integer *qptr, integer *prmptr, integer *perm, integer *
	givptr, integer *givcol, real *givnum, real *work, integer *iwork, 
	integer *info)
{
    /* System generated locals */
    integer q_dim1, q_offset, i__1, i__2;

    /* Builtin functions */
    integer pow_ii(integer *, integer *);

    /* Local variables */
    integer i__, k, n1, n2, is, iw, iz, iq2, ptr, ldq2, indx, curr, indxc;
    extern /* Subroutine */ int sgemm_(char *, char *, integer *, integer *, 
	    integer *, real *, real *, integer *, real *, integer *, real *, 
	    real *, integer *);
    integer indxp;
    extern /* Subroutine */ int slaed8_(integer *, integer *, integer *, 
	    integer *, real *, real *, integer *, integer *, real *, integer *
, real *, real *, real *, integer *, real *, integer *, integer *, 
	     integer *, real *, integer *, integer *, integer *), slaed9_(
	    integer *, integer *, integer *, integer *, real *, real *, 
	    integer *, real *, real *, real *, real *, integer *, integer *), 
	    slaeda_(integer *, integer *, integer *, integer *, integer *, 
	    integer *, integer *, integer *, real *, real *, integer *, real *
, real *, integer *);
    integer idlmda;
    extern /* Subroutine */ int xerbla_(char *, integer *), slamrg_(
	    integer *, integer *, real *, integer *, integer *, integer *);
    integer coltyp;


/*  -- LAPACK routine (version 3.1) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */

/*     .. Scalar Arguments .. */
/*     .. */
/*     .. Array Arguments .. */
/*     .. */

/*  Purpose */
/*  ======= */

/*  SLAED7 computes the updated eigensystem of a diagonal */
/*  matrix after modification by a rank-one symmetric matrix. This */
/*  routine is used only for the eigenproblem which requires all */
/*  eigenvalues and optionally eigenvectors of a dense symmetric matrix */
/*  that has been reduced to tridiagonal form.  SLAED1 handles */
/*  the case in which all eigenvalues and eigenvectors of a symmetric */
/*  tridiagonal matrix are desired. */

/*    T = Q(in) ( D(in) + RHO * Z*Z' ) Q'(in) = Q(out) * D(out) * Q'(out) */

/*     where Z = Q'u, u is a vector of length N with ones in the */
/*     CUTPNT and CUTPNT + 1 th elements and zeros elsewhere. */

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

/*        The first stage consists of deflating the size of the problem */
/*        when there are multiple eigenvalues or if there is a zero in */
/*        the Z vector.  For each such occurence the dimension of the */
/*        secular equation problem is reduced by one.  This stage is */
/*        performed by the routine SLAED8. */

/*        The second stage consists of calculating the updated */
/*        eigenvalues. This is done by finding the roots of the secular */
/*        equation via the routine SLAED4 (as called by SLAED9). */
/*        This routine also calculates the eigenvectors of the current */
/*        problem. */

/*        The final stage consists of computing the updated eigenvectors */
/*        directly using the updated eigenvalues.  The eigenvectors for */
/*        the current problem are multiplied with the eigenvectors from */
/*        the overall problem. */

/*  Arguments */
/*  ========= */

/*  ICOMPQ  (input) INTEGER */
/*          = 0:  Compute eigenvalues only. */
/*          = 1:  Compute eigenvectors of original dense symmetric matrix */
/*                also.  On entry, Q contains the orthogonal matrix used */
/*                to reduce the original matrix to tridiagonal form. */

/*  N      (input) INTEGER */
/*         The dimension of the symmetric tridiagonal matrix.  N >= 0. */

/*  QSIZ   (input) INTEGER */
/*         The dimension of the orthogonal matrix used to reduce */
/*         the full matrix to tridiagonal form.  QSIZ >= N if ICOMPQ = 1. */

/*  TLVLS  (input) INTEGER */
/*         The total number of merging levels in the overall divide and */
/*         conquer tree. */

/*  CURLVL (input) INTEGER */
/*         The current level in the overall merge routine, */
/*         0 <= CURLVL <= TLVLS. */

/*  CURPBM (input) INTEGER */
/*         The current problem in the current level in the overall */
/*         merge routine (counting from upper left to lower right). */

/*  D      (input/output) REAL array, dimension (N) */
/*         On entry, the eigenvalues of the rank-1-perturbed matrix. */
/*         On exit, the eigenvalues of the repaired matrix. */

/*  Q      (input/output) REAL array, dimension (LDQ, N) */
/*         On entry, the eigenvectors of the rank-1-perturbed matrix. */
/*         On exit, the eigenvectors of the repaired tridiagonal matrix. */

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

/*  INDXQ  (output) INTEGER array, dimension (N) */
/*         The permutation which will reintegrate the subproblem just */
/*         solved back into sorted order, i.e., D( INDXQ( I = 1, N ) ) */
/*         will be in ascending order. */

/*  RHO    (input) REAL */
/*         The subdiagonal element used to create the rank-1 */
/*         modification. */

/*  CUTPNT (input) INTEGER */
/*         Contains the location of the last eigenvalue in the leading */
/*         sub-matrix.  min(1,N) <= CUTPNT <= N. */

/*  QSTORE (input/output) REAL array, dimension (N**2+1) */
/*         Stores eigenvectors of submatrices encountered during */
/*         divide and conquer, packed together. QPTR points to */
/*         beginning of the submatrices. */

/*  QPTR   (input/output) INTEGER array, dimension (N+2) */
/*         List of indices pointing to beginning of submatrices stored */
/*         in QSTORE. The submatrices are numbered starting at the */
/*         bottom left of the divide and conquer tree, from left to */
/*         right and bottom to top. */

/*  PRMPTR (input) INTEGER array, dimension (N lg N) */
/*         Contains a list of pointers which indicate where in PERM a */
/*         level's permutation is stored.  PRMPTR(i+1) - PRMPTR(i) */
/*         indicates the size of the permutation and also the size of */
/*         the full, non-deflated problem. */

/*  PERM   (input) INTEGER array, dimension (N lg N) */
/*         Contains the permutations (from deflation and sorting) to be */
/*         applied to each eigenblock. */

/*  GIVPTR (input) INTEGER array, dimension (N lg N) */
/*         Contains a list of pointers which indicate where in GIVCOL a */
/*         level's Givens rotations are stored.  GIVPTR(i+1) - GIVPTR(i) */
/*         indicates the number of Givens rotations. */

/*  GIVCOL (input) INTEGER array, dimension (2, N lg N) */
/*         Each pair of numbers indicates a pair of columns to take place */
/*         in a Givens rotation. */

/*  GIVNUM (input) REAL array, dimension (2, N lg N) */
/*         Each number indicates the S value to be used in the */
/*         corresponding Givens rotation. */

/*  WORK   (workspace) REAL array, dimension (3*N+QSIZ*N) */

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

/*  INFO   (output) INTEGER */
/*          = 0:  successful exit. */
/*          < 0:  if INFO = -i, the i-th argument had an illegal value. */
/*          > 0:  if INFO = 1, an eigenvalue did not converge */

/*  Further Details */
/*  =============== */

/*  Based on contributions by */
/*     Jeff Rutter, Computer Science Division, University of California */
/*     at Berkeley, USA */

/*  ===================================================================== */

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Intrinsic Functions .. */
/*     .. */
/*     .. Executable Statements .. */

/*     Test the input parameters. */

    /* Parameter adjustments */
    --d__;
    q_dim1 = *ldq;
    q_offset = 1 + q_dim1;
    q -= q_offset;
    --indxq;
    --qstore;
    --qptr;
    --prmptr;
    --perm;
    --givptr;
    givcol -= 3;
    givnum -= 3;
    --work;
    --iwork;

    /* Function Body */
    *info = 0;

    if (*icompq < 0 || *icompq > 1) {
	*info = -1;
    } else if (*n < 0) {
	*info = -2;
    } else if (*icompq == 1 && *qsiz < *n) {
	*info = -4;
    } else if (*ldq < max(1,*n)) {
	*info = -9;
    } else if (min(1,*n) > *cutpnt || *n < *cutpnt) {
	*info = -12;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("SLAED7", &i__1);
	return 0;
    }

/*     Quick return if possible */

    if (*n == 0) {
	return 0;
    }

/*     The following values are for bookkeeping purposes only.  They are */
/*     integer pointers which indicate the portion of the workspace */
/*     used by a particular array in SLAED8 and SLAED9. */

    if (*icompq == 1) {
	ldq2 = *qsiz;
    } else {
	ldq2 = *n;
    }

    iz = 1;
    idlmda = iz + *n;
    iw = idlmda + *n;
    iq2 = iw + *n;
    is = iq2 + *n * ldq2;

    indx = 1;
    indxc = indx + *n;
    coltyp = indxc + *n;
    indxp = coltyp + *n;

/*     Form the z-vector which consists of the last row of Q_1 and the */
/*     first row of Q_2. */

    ptr = pow_ii(&c__2, tlvls) + 1;
    i__1 = *curlvl - 1;
    for (i__ = 1; i__ <= i__1; ++i__) {
	i__2 = *tlvls - i__;
	ptr += pow_ii(&c__2, &i__2);
/* L10: */
    }
    curr = ptr + *curpbm;
    slaeda_(n, tlvls, curlvl, curpbm, &prmptr[1], &perm[1], &givptr[1], &
	    givcol[3], &givnum[3], &qstore[1], &qptr[1], &work[iz], &work[iz 
	    + *n], info);

/*     When solving the final problem, we no longer need the stored data, */
/*     so we will overwrite the data from this level onto the previously */
/*     used storage space. */

    if (*curlvl == *tlvls) {
	qptr[curr] = 1;
	prmptr[curr] = 1;
	givptr[curr] = 1;
    }

/*     Sort and Deflate eigenvalues. */

    slaed8_(icompq, &k, n, qsiz, &d__[1], &q[q_offset], ldq, &indxq[1], rho, 
	    cutpnt, &work[iz], &work[idlmda], &work[iq2], &ldq2, &work[iw], &
	    perm[prmptr[curr]], &givptr[curr + 1], &givcol[(givptr[curr] << 1)
	     + 1], &givnum[(givptr[curr] << 1) + 1], &iwork[indxp], &iwork[
	    indx], info);
    prmptr[curr + 1] = prmptr[curr] + *n;
    givptr[curr + 1] += givptr[curr];

/*     Solve Secular Equation. */

    if (k != 0) {
	slaed9_(&k, &c__1, &k, n, &d__[1], &work[is], &k, rho, &work[idlmda], 
		&work[iw], &qstore[qptr[curr]], &k, info);
	if (*info != 0) {
	    goto L30;
	}
	if (*icompq == 1) {
	    sgemm_("N", "N", qsiz, &k, &k, &c_b10, &work[iq2], &ldq2, &qstore[
		    qptr[curr]], &k, &c_b11, &q[q_offset], ldq);
	}
/* Computing 2nd power */
	i__1 = k;
	qptr[curr + 1] = qptr[curr] + i__1 * i__1;

/*     Prepare the INDXQ sorting permutation. */

	n1 = k;
	n2 = *n - k;
	slamrg_(&n1, &n2, &d__[1], &c__1, &c_n1, &indxq[1]);
    } else {
	qptr[curr + 1] = qptr[curr];
	i__1 = *n;
	for (i__ = 1; i__ <= i__1; ++i__) {
	    indxq[i__] = i__;
/* L20: */
	}
    }

L30:
    return 0;

/*     End of SLAED7 */

} /* slaed7_ */