/* ./src_f77/zlapll.f -- translated by f2c (version 20030320).
   You must link the resulting object file with the libraries:
	-lf2c -lm   (in that order)
*/

#include <punc/vf2c.h>

/* Subroutine */ int zlapll_(integer *n, doublecomplex *x, integer *incx, 
	doublecomplex *y, integer *incy, doublereal *ssmin)
{
    /* System generated locals */
    integer i__1;
    doublereal d__1, d__2, d__3;
    doublecomplex z__1, z__2, z__3, z__4;

    /* Builtin functions */
    void d_cnjg(doublecomplex *, doublecomplex *);
    double z_abs(doublecomplex *);

    /* Local variables */
    static doublecomplex c__, a11, a12, a22, tau;
    extern /* Subroutine */ int dlas2_(doublereal *, doublereal *, doublereal 
	    *, doublereal *, doublereal *);
    extern /* Double Complex */ VOID zdotc_(doublecomplex *, integer *, 
	    doublecomplex *, integer *, doublecomplex *, integer *);
    static doublereal ssmax;
    extern /* Subroutine */ int zaxpy_(integer *, doublecomplex *, 
	    doublecomplex *, integer *, doublecomplex *, integer *), zlarfg_(
	    integer *, doublecomplex *, doublecomplex *, integer *, 
	    doublecomplex *);


/*  -- LAPACK auxiliary routine (version 3.0) -- */
/*     Univ. of Tennessee, Univ. of California Berkeley, NAG Ltd., */
/*     Courant Institute, Argonne National Lab, and Rice University */
/*     September 30, 1994 */

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

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

/*  Given two column vectors X and Y, let */

/*                       A = ( X Y ). */

/*  The subroutine first computes the QR factorization of A = Q*R, */
/*  and then computes the SVD of the 2-by-2 upper triangular matrix R. */
/*  The smaller singular value of R is returned in SSMIN, which is used */
/*  as the measurement of the linear dependency of the vectors X and Y. */

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

/*  N       (input) INTEGER */
/*          The length of the vectors X and Y. */

/*  X       (input/output) COMPLEX*16 array, dimension (1+(N-1)*INCX) */
/*          On entry, X contains the N-vector X. */
/*          On exit, X is overwritten. */

/*  INCX    (input) INTEGER */
/*          The increment between successive elements of X. INCX > 0. */

/*  Y       (input/output) COMPLEX*16 array, dimension (1+(N-1)*INCY) */
/*          On entry, Y contains the N-vector Y. */
/*          On exit, Y is overwritten. */

/*  INCY    (input) INTEGER */
/*          The increment between successive elements of Y. INCY > 0. */

/*  SSMIN   (output) DOUBLE PRECISION */
/*          The smallest singular value of the N-by-2 matrix A = ( X Y ). */

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

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

/*     Quick return if possible */

    /* Parameter adjustments */
    --y;
    --x;

    /* Function Body */
    if (*n <= 1) {
	*ssmin = 0.;
	return 0;
    }

/*     Compute the QR factorization of the N-by-2 matrix ( X Y ) */

    zlarfg_(n, &x[1], &x[*incx + 1], incx, &tau);
    a11.r = x[1].r, a11.i = x[1].i;
    x[1].r = 1., x[1].i = 0.;

    d_cnjg(&z__3, &tau);
    z__2.r = -z__3.r, z__2.i = -z__3.i;
    zdotc_(&z__4, n, &x[1], incx, &y[1], incy);
    z__1.r = z__2.r * z__4.r - z__2.i * z__4.i, z__1.i = z__2.r * z__4.i + 
	    z__2.i * z__4.r;
    c__.r = z__1.r, c__.i = z__1.i;
    zaxpy_(n, &c__, &x[1], incx, &y[1], incy);

    i__1 = *n - 1;
    zlarfg_(&i__1, &y[*incy + 1], &y[(*incy << 1) + 1], incy, &tau);

    a12.r = y[1].r, a12.i = y[1].i;
    i__1 = *incy + 1;
    a22.r = y[i__1].r, a22.i = y[i__1].i;

/*     Compute the SVD of 2-by-2 Upper triangular matrix. */

    d__1 = z_abs(&a11);
    d__2 = z_abs(&a12);
    d__3 = z_abs(&a22);
    dlas2_(&d__1, &d__2, &d__3, ssmin, &ssmax);

    return 0;

/*     End of ZLAPLL */

} /* zlapll_ */

