sorgl2.c

#include "clapack.h"

/* Subroutine */ int sorgl2_(integer *m, integer *n, integer *k, real *a, 
	integer *lda, real *tau, real *work, integer *info)
{
    /* System generated locals */
    integer a_dim1, a_offset, i__1, i__2;
    real r__1;

    /* Local variables */
    integer i__, j, l;
    extern /* Subroutine */ int sscal_(integer *, real *, real *, integer *), 
	    slarf_(char *, integer *, integer *, real *, integer *, real *, 
	    real *, integer *, real *), xerbla_(char *, integer *);


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

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

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

/*  SORGL2 generates an m by n real matrix Q with orthonormal rows, */
/*  which is defined as the first m rows of a product of k elementary */
/*  reflectors of order n */

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

/*  as returned by SGELQF. */

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

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

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

/*  K       (input) INTEGER */
/*          The number of elementary reflectors whose product defines the */
/*          matrix Q. M >= K >= 0. */

/*  A       (input/output) REAL array, dimension (LDA,N) */
/*          On entry, the i-th row must contain the vector which defines */
/*          the elementary reflector H(i), for i = 1,2,...,k, as returned */
/*          by SGELQF in the first k rows of its array argument A. */
/*          On exit, the m-by-n matrix Q. */

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

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

/*  WORK    (workspace) REAL array, dimension (M) */

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

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

/*     .. Parameters .. */
/*     .. */
/*     .. Local Scalars .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. 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;
    if (*m < 0) {
	*info = -1;
    } else if (*n < *m) {
	*info = -2;
    } else if (*k < 0 || *k > *m) {
	*info = -3;
    } else if (*lda < max(1,*m)) {
	*info = -5;
    }
    if (*info != 0) {
	i__1 = -(*info);
	xerbla_("SORGL2", &i__1);
	return 0;
    }

/*     Quick return if possible */

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

    if (*k < *m) {

/*        Initialise rows k+1:m to rows of the unit matrix */

	i__1 = *n;
	for (j = 1; j <= i__1; ++j) {
	    i__2 = *m;
	    for (l = *k + 1; l <= i__2; ++l) {
		a[l + j * a_dim1] = 0.f;
/* L10: */
	    }
	    if (j > *k && j <= *m) {
		a[j + j * a_dim1] = 1.f;
	    }
/* L20: */
	}
    }

    for (i__ = *k; i__ >= 1; --i__) {

/*        Apply H(i) to A(i:m,i:n) from the right */

	if (i__ < *n) {
	    if (i__ < *m) {
		a[i__ + i__ * a_dim1] = 1.f;
		i__1 = *m - i__;
		i__2 = *n - i__ + 1;
		slarf_("Right", &i__1, &i__2, &a[i__ + i__ * a_dim1], lda, &
			tau[i__], &a[i__ + 1 + i__ * a_dim1], lda, &work[1]);
	    }
	    i__1 = *n - i__;
	    r__1 = -tau[i__];
	    sscal_(&i__1, &r__1, &a[i__ + (i__ + 1) * a_dim1], lda);
	}
	a[i__ + i__ * a_dim1] = 1.f - tau[i__];

/*        Set A(i,1:i-1) to zero */

	i__1 = i__ - 1;
	for (l = 1; l <= i__1; ++l) {
	    a[i__ + l * a_dim1] = 0.f;
/* L30: */
	}
/* L40: */
    }
    return 0;

/*     End of SORGL2 */

} /* sorgl2_ */