sorghr.c

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/* sorghr.f -- translated by f2c (version 20061008).
   You must link the resulting object file with libf2c:
        on Microsoft Windows system, link with libf2c.lib;
        on Linux or Unix systems, link with .../path/to/libf2c.a -lm
        or, if you install libf2c.a in a standard place, with -lf2c -lm
        -- in that order, at the end of the command line, as in
                cc *.o -lf2c -lm
        Source for libf2c is in /netlib/f2c/libf2c.zip, e.g.,

                http://www.netlib.org/f2c/libf2c.zip
*/

#include "f2c.h"
#include "blaswrap.h"

/* Table of constant values */

static integer c__1 = 1;
static integer c_n1 = -1;

/* Subroutine */ int sorghr_(integer *n, integer *ilo, integer *ihi, real *a, 
        integer *lda, real *tau, real *work, integer *lwork, integer *info)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2;

    /* Local variables */
    integer i__, j, nb, nh, iinfo;
    extern /* Subroutine */ int xerbla_(char *, integer *);
    extern integer ilaenv_(integer *, char *, char *, integer *, integer *, 
            integer *, integer *);
    extern /* Subroutine */ int sorgqr_(integer *, integer *, integer *, real 
            *, integer *, real *, real *, integer *, integer *);
    integer lwkopt;
    logical lquery;


/*  -- LAPACK routine (version 3.2) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley and NAG Ltd.. */
/*     November 2006 */

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

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

/*  SORGHR generates a real orthogonal matrix Q which is defined as the */
/*  product of IHI-ILO elementary reflectors of order N, as returned by */
/*  SGEHRD: */

/*  Q = H(ilo) H(ilo+1) . . . H(ihi-1). */

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

/*  N       (input) INTEGER */
/*          The order of the matrix Q. N >= 0. */

/*  ILO     (input) INTEGER */
/*  IHI     (input) INTEGER */
/*          ILO and IHI must have the same values as in the previous call */
/*          of SGEHRD. Q is equal to the unit matrix except in the */
/*          submatrix Q(ilo+1:ihi,ilo+1:ihi). */
/*          1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0. */

/*  A       (input/output) REAL array, dimension (LDA,N) */
/*          On entry, the vectors which define the elementary reflectors, */
/*          as returned by SGEHRD. */
/*          On exit, the N-by-N orthogonal matrix Q. */

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

/*  TAU     (input) REAL array, dimension (N-1) */
/*          TAU(i) must contain the scalar factor of the elementary */
/*          reflector H(i), as returned by SGEHRD. */

/*  WORK    (workspace/output) REAL array, dimension (MAX(1,LWORK)) */
/*          On exit, if INFO = 0, WORK(1) returns the optimal LWORK. */

/*  LWORK   (input) INTEGER */
/*          The dimension of the array WORK. LWORK >= IHI-ILO. */
/*          For optimum performance LWORK >= (IHI-ILO)*NB, where NB is */
/*          the optimal blocksize. */

/*          If LWORK = -1, then a workspace query is assumed; the routine */
/*          only calculates the optimal size of the WORK array, returns */
/*          this value as the first entry of the WORK array, and no error */
/*          message related to LWORK is issued by XERBLA. */

/*  INFO    (output) INTEGER */
/*          = 0:  successful exit */
/*          < 0:  if INFO = -i, the i-th argument had an illegal value */

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

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

/*     Test the input arguments */

    /* Parameter adjustments */
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;
    --tau;
    --work;

    /* Function Body */
    *info = 0;
    nh = *ihi - *ilo;
    lquery = *lwork == -1;
    if (*n < 0) {
        *info = -1;
    } else if (*ilo < 1 || *ilo > max(1,*n)) {
        *info = -2;
    } else if (*ihi < min(*ilo,*n) || *ihi > *n) {
        *info = -3;
    } else if (*lda < max(1,*n)) {
        *info = -5;
    } else if (*lwork < max(1,nh) && ! lquery) {
        *info = -8;
    }

    if (*info == 0) {
        nb = ilaenv_(&c__1, "SORGQR", " ", &nh, &nh, &nh, &c_n1);
        lwkopt = max(1,nh) * nb;
        work[1] = (real) lwkopt;
    }

    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("SORGHR", &i__1);
        return 0;
    } else if (lquery) {
        return 0;
    }

/*     Quick return if possible */

    if (*n == 0) {
        work[1] = 1.f;
        return 0;
    }

/*     Shift the vectors which define the elementary reflectors one */
/*     column to the right, and set the first ilo and the last n-ihi */
/*     rows and columns to those of the unit matrix */

    i__1 = *ilo + 1;
    for (j = *ihi; j >= i__1; --j) {
        i__2 = j - 1;
        for (i__ = 1; i__ <= i__2; ++i__) {
            a[i__ + j * a_dim1] = 0.f;
/* L10: */
        }
        i__2 = *ihi;
        for (i__ = j + 1; i__ <= i__2; ++i__) {
            a[i__ + j * a_dim1] = a[i__ + (j - 1) * a_dim1];
/* L20: */
        }
        i__2 = *n;
        for (i__ = *ihi + 1; i__ <= i__2; ++i__) {
            a[i__ + j * a_dim1] = 0.f;
/* L30: */
        }
/* L40: */
    }
    i__1 = *ilo;
    for (j = 1; j <= i__1; ++j) {
        i__2 = *n;
        for (i__ = 1; i__ <= i__2; ++i__) {
            a[i__ + j * a_dim1] = 0.f;
/* L50: */
        }
        a[j + j * a_dim1] = 1.f;
/* L60: */
    }
    i__1 = *n;
    for (j = *ihi + 1; j <= i__1; ++j) {
        i__2 = *n;
        for (i__ = 1; i__ <= i__2; ++i__) {
            a[i__ + j * a_dim1] = 0.f;
/* L70: */
        }
        a[j + j * a_dim1] = 1.f;
/* L80: */
    }

    if (nh > 0) {

/*        Generate Q(ilo+1:ihi,ilo+1:ihi) */

        sorgqr_(&nh, &nh, &nh, &a[*ilo + 1 + (*ilo + 1) * a_dim1], lda, &tau[*
                ilo], &work[1], lwork, &iinfo);
    }
    work[1] = (real) lwkopt;
    return 0;

/*     End of SORGHR */

} /* sorghr_ */