dorm2l.c

Go to the documentation of this file.

/* dorm2l.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;

/* Subroutine */ int dorm2l_(char *side, char *trans, integer *m, integer *n, 
        integer *k, doublereal *a, integer *lda, doublereal *tau, doublereal *
        c__, integer *ldc, doublereal *work, integer *info)
{
    /* System generated locals */
    integer a_dim1, a_offset, c_dim1, c_offset, i__1, i__2;

    /* Local variables */
    integer i__, i1, i2, i3, mi, ni, nq;
    doublereal aii;
    logical left;
    extern /* Subroutine */ int dlarf_(char *, integer *, integer *, 
            doublereal *, integer *, doublereal *, doublereal *, integer *, 
            doublereal *);
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int xerbla_(char *, integer *);
    logical notran;


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

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

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

/*  DORM2L overwrites the general real m by n matrix C with */

/*        Q * C  if SIDE = 'L' and TRANS = 'N', or */

/*        Q'* C  if SIDE = 'L' and TRANS = 'T', or */

/*        C * Q  if SIDE = 'R' and TRANS = 'N', or */

/*        C * Q' if SIDE = 'R' and TRANS = 'T', */

/*  where Q is a real orthogonal matrix defined as the product of k */
/*  elementary reflectors */

/*        Q = H(k) . . . H(2) H(1) */

/*  as returned by DGEQLF. Q is of order m if SIDE = 'L' and of order n */
/*  if SIDE = 'R'. */

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

/*  SIDE    (input) CHARACTER*1 */
/*          = 'L': apply Q or Q' from the Left */
/*          = 'R': apply Q or Q' from the Right */

/*  TRANS   (input) CHARACTER*1 */
/*          = 'N': apply Q  (No transpose) */
/*          = 'T': apply Q' (Transpose) */

/*  M       (input) INTEGER */
/*          The number of rows of the matrix C. M >= 0. */

/*  N       (input) INTEGER */
/*          The number of columns of the matrix C. N >= 0. */

/*  K       (input) INTEGER */
/*          The number of elementary reflectors whose product defines */
/*          the matrix Q. */
/*          If SIDE = 'L', M >= K >= 0; */
/*          if SIDE = 'R', N >= K >= 0. */

/*  A       (input) DOUBLE PRECISION array, dimension (LDA,K) */
/*          The i-th column must contain the vector which defines the */
/*          elementary reflector H(i), for i = 1,2,...,k, as returned by */
/*          DGEQLF in the last k columns of its array argument A. */
/*          A is modified by the routine but restored on exit. */

/*  LDA     (input) INTEGER */
/*          The leading dimension of the array A. */
/*          If SIDE = 'L', LDA >= max(1,M); */
/*          if SIDE = 'R', LDA >= max(1,N). */

/*  TAU     (input) DOUBLE PRECISION array, dimension (K) */
/*          TAU(i) must contain the scalar factor of the elementary */
/*          reflector H(i), as returned by DGEQLF. */

/*  C       (input/output) DOUBLE PRECISION array, dimension (LDC,N) */
/*          On entry, the m by n matrix C. */
/*          On exit, C is overwritten by Q*C or Q'*C or C*Q' or C*Q. */

/*  LDC     (input) INTEGER */
/*          The leading dimension of the array C. LDC >= max(1,M). */

/*  WORK    (workspace) DOUBLE PRECISION array, dimension */
/*                                   (N) if SIDE = 'L', */
/*                                   (M) if SIDE = 'R' */

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

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

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

/*     Test the input arguments */

    /* Parameter adjustments */
    a_dim1 = *lda;
    a_offset = 1 + a_dim1;
    a -= a_offset;
    --tau;
    c_dim1 = *ldc;
    c_offset = 1 + c_dim1;
    c__ -= c_offset;
    --work;

    /* Function Body */
    *info = 0;
    left = lsame_(side, "L");
    notran = lsame_(trans, "N");

/*     NQ is the order of Q */

    if (left) {
        nq = *m;
    } else {
        nq = *n;
    }
    if (! left && ! lsame_(side, "R")) {
        *info = -1;
    } else if (! notran && ! lsame_(trans, "T")) {
        *info = -2;
    } else if (*m < 0) {
        *info = -3;
    } else if (*n < 0) {
        *info = -4;
    } else if (*k < 0 || *k > nq) {
        *info = -5;
    } else if (*lda < max(1,nq)) {
        *info = -7;
    } else if (*ldc < max(1,*m)) {
        *info = -10;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("DORM2L", &i__1);
        return 0;
    }

/*     Quick return if possible */

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

    if (left && notran || ! left && ! notran) {
        i1 = 1;
        i2 = *k;
        i3 = 1;
    } else {
        i1 = *k;
        i2 = 1;
        i3 = -1;
    }

    if (left) {
        ni = *n;
    } else {
        mi = *m;
    }

    i__1 = i2;
    i__2 = i3;
    for (i__ = i1; i__2 < 0 ? i__ >= i__1 : i__ <= i__1; i__ += i__2) {
        if (left) {

/*           H(i) is applied to C(1:m-k+i,1:n) */

            mi = *m - *k + i__;
        } else {

/*           H(i) is applied to C(1:m,1:n-k+i) */

            ni = *n - *k + i__;
        }

/*        Apply H(i) */

        aii = a[nq - *k + i__ + i__ * a_dim1];
        a[nq - *k + i__ + i__ * a_dim1] = 1.;
        dlarf_(side, &mi, &ni, &a[i__ * a_dim1 + 1], &c__1, &tau[i__], &c__[
                c_offset], ldc, &work[1]);
        a[nq - *k + i__ + i__ * a_dim1] = aii;
/* L10: */
    }
    return 0;

/*     End of DORM2L */

} /* dorm2l_ */