drzt01.c

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/* drzt01.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__8 = 8;
static doublereal c_b6 = 0.;
static doublereal c_b13 = -1.;
static integer c__1 = 1;

doublereal drzt01_(integer *m, integer *n, doublereal *a, doublereal *af, 
        integer *lda, doublereal *tau, doublereal *work, integer *lwork)
{
    /* System generated locals */
    integer a_dim1, a_offset, af_dim1, af_offset, i__1, i__2;
    doublereal ret_val;

    /* Local variables */
    integer i__, j, info;
    doublereal norma;
    extern /* Subroutine */ int daxpy_(integer *, doublereal *, doublereal *, 
            integer *, doublereal *, integer *);
    doublereal rwork[1];
    extern doublereal dlamch_(char *), dlange_(char *, integer *, 
            integer *, doublereal *, integer *, doublereal *);
    extern /* Subroutine */ int dlaset_(char *, integer *, integer *, 
            doublereal *, doublereal *, doublereal *, integer *), 
            xerbla_(char *, integer *), dormrz_(char *, char *, 
            integer *, integer *, integer *, integer *, doublereal *, integer 
            *, doublereal *, doublereal *, integer *, doublereal *, integer *, 
             integer *);


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

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

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

/*  DRZT01 returns */
/*       || A - R*Q || / ( M * eps * ||A|| ) */
/*  for an upper trapezoidal A that was factored with DTZRZF. */

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

/*  M       (input) INTEGER */
/*          The number of rows of the matrices A and AF. */

/*  N       (input) INTEGER */
/*          The number of columns of the matrices A and AF. */

/*  A       (input) DOUBLE PRECISION array, dimension (LDA,N) */
/*          The original upper trapezoidal M by N matrix A. */

/*  AF      (input) DOUBLE PRECISION array, dimension (LDA,N) */
/*          The output of DTZRZF for input matrix A. */
/*          The lower triangle is not referenced. */

/*  LDA     (input) INTEGER */
/*          The leading dimension of the arrays A and AF. */

/*  TAU     (input) DOUBLE PRECISION array, dimension (M) */
/*          Details of the Householder transformations as returned by */
/*          DTZRZF. */

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

/*  LWORK   (input) INTEGER */
/*          The length of the array WORK.  LWORK >= m*n + m*nb. */

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

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

    /* Parameter adjustments */
    af_dim1 = *lda;
    af_offset = 1 + af_dim1;
    af -= af_offset;
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;
    --tau;
    --work;

    /* Function Body */
    ret_val = 0.;

    if (*lwork < *m * *n + *m) {
        xerbla_("DRZT01", &c__8);
        return ret_val;
    }

/*     Quick return if possible */

    if (*m <= 0 || *n <= 0) {
        return ret_val;
    }

    norma = dlange_("One-norm", m, n, &a[a_offset], lda, rwork);

/*     Copy upper triangle R */

    dlaset_("Full", m, n, &c_b6, &c_b6, &work[1], m);
    i__1 = *m;
    for (j = 1; j <= i__1; ++j) {
        i__2 = j;
        for (i__ = 1; i__ <= i__2; ++i__) {
            work[(j - 1) * *m + i__] = af[i__ + j * af_dim1];
/* L10: */
        }
/* L20: */
    }

/*     R = R * P(1) * ... *P(m) */

    i__1 = *n - *m;
    i__2 = *lwork - *m * *n;
    dormrz_("Right", "No tranpose", m, n, m, &i__1, &af[af_offset], lda, &tau[
            1], &work[1], m, &work[*m * *n + 1], &i__2, &info);

/*     R = R - A */

    i__1 = *n;
    for (i__ = 1; i__ <= i__1; ++i__) {
        daxpy_(m, &c_b13, &a[i__ * a_dim1 + 1], &c__1, &work[(i__ - 1) * *m + 
                1], &c__1);
/* L30: */
    }

    ret_val = dlange_("One-norm", m, n, &work[1], m, rwork);

    ret_val /= dlamch_("Epsilon") * (doublereal) max(*m,*n);
    if (norma != 0.) {
        ret_val /= norma;
    }

    return ret_val;

/*     End of DRZT01 */

} /* drzt01_ */