ztrexc.c

Go to the documentation of this file.

/* ztrexc.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 ztrexc_(char *compq, integer *n, doublecomplex *t, 
        integer *ldt, doublecomplex *q, integer *ldq, integer *ifst, integer *
        ilst, integer *info)
{
    /* System generated locals */
    integer q_dim1, q_offset, t_dim1, t_offset, i__1, i__2, i__3;
    doublecomplex z__1;

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

    /* Local variables */
    integer k, m1, m2, m3;
    doublereal cs;
    doublecomplex t11, t22, sn, temp;
    extern /* Subroutine */ int zrot_(integer *, doublecomplex *, integer *, 
            doublecomplex *, integer *, doublereal *, doublecomplex *);
    extern logical lsame_(char *, char *);
    logical wantq;
    extern /* Subroutine */ int xerbla_(char *, integer *), zlartg_(
            doublecomplex *, doublecomplex *, doublereal *, doublecomplex *, 
            doublecomplex *);


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

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

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

/*  ZTREXC reorders the Schur factorization of a complex matrix */
/*  A = Q*T*Q**H, so that the diagonal element of T with row index IFST */
/*  is moved to row ILST. */

/*  The Schur form T is reordered by a unitary similarity transformation */
/*  Z**H*T*Z, and optionally the matrix Q of Schur vectors is updated by */
/*  postmultplying it with Z. */

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

/*  COMPQ   (input) CHARACTER*1 */
/*          = 'V':  update the matrix Q of Schur vectors; */
/*          = 'N':  do not update Q. */

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

/*  T       (input/output) COMPLEX*16 array, dimension (LDT,N) */
/*          On entry, the upper triangular matrix T. */
/*          On exit, the reordered upper triangular matrix. */

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

/*  Q       (input/output) COMPLEX*16 array, dimension (LDQ,N) */
/*          On entry, if COMPQ = 'V', the matrix Q of Schur vectors. */
/*          On exit, if COMPQ = 'V', Q has been postmultiplied by the */
/*          unitary transformation matrix Z which reorders T. */
/*          If COMPQ = 'N', Q is not referenced. */

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

/*  IFST    (input) INTEGER */
/*  ILST    (input) INTEGER */
/*          Specify the reordering of the diagonal elements of T: */
/*          The element with row index IFST is moved to row ILST by a */
/*          sequence of transpositions between adjacent elements. */
/*          1 <= IFST <= N; 1 <= ILST <= N. */

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

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

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

/*     Decode and test the input parameters. */

    /* Parameter adjustments */
    t_dim1 = *ldt;
    t_offset = 1 + t_dim1;
    t -= t_offset;
    q_dim1 = *ldq;
    q_offset = 1 + q_dim1;
    q -= q_offset;

    /* Function Body */
    *info = 0;
    wantq = lsame_(compq, "V");
    if (! lsame_(compq, "N") && ! wantq) {
        *info = -1;
    } else if (*n < 0) {
        *info = -2;
    } else if (*ldt < max(1,*n)) {
        *info = -4;
    } else if (*ldq < 1 || wantq && *ldq < max(1,*n)) {
        *info = -6;
    } else if (*ifst < 1 || *ifst > *n) {
        *info = -7;
    } else if (*ilst < 1 || *ilst > *n) {
        *info = -8;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("ZTREXC", &i__1);
        return 0;
    }

/*     Quick return if possible */

    if (*n == 1 || *ifst == *ilst) {
        return 0;
    }

    if (*ifst < *ilst) {

/*        Move the IFST-th diagonal element forward down the diagonal. */

        m1 = 0;
        m2 = -1;
        m3 = 1;
    } else {

/*        Move the IFST-th diagonal element backward up the diagonal. */

        m1 = -1;
        m2 = 0;
        m3 = -1;
    }

    i__1 = *ilst + m2;
    i__2 = m3;
    for (k = *ifst + m1; i__2 < 0 ? k >= i__1 : k <= i__1; k += i__2) {

/*        Interchange the k-th and (k+1)-th diagonal elements. */

        i__3 = k + k * t_dim1;
        t11.r = t[i__3].r, t11.i = t[i__3].i;
        i__3 = k + 1 + (k + 1) * t_dim1;
        t22.r = t[i__3].r, t22.i = t[i__3].i;

/*        Determine the transformation to perform the interchange. */

        z__1.r = t22.r - t11.r, z__1.i = t22.i - t11.i;
        zlartg_(&t[k + (k + 1) * t_dim1], &z__1, &cs, &sn, &temp);

/*        Apply transformation to the matrix T. */

        if (k + 2 <= *n) {
            i__3 = *n - k - 1;
            zrot_(&i__3, &t[k + (k + 2) * t_dim1], ldt, &t[k + 1 + (k + 2) * 
                    t_dim1], ldt, &cs, &sn);
        }
        i__3 = k - 1;
        d_cnjg(&z__1, &sn);
        zrot_(&i__3, &t[k * t_dim1 + 1], &c__1, &t[(k + 1) * t_dim1 + 1], &
                c__1, &cs, &z__1);

        i__3 = k + k * t_dim1;
        t[i__3].r = t22.r, t[i__3].i = t22.i;
        i__3 = k + 1 + (k + 1) * t_dim1;
        t[i__3].r = t11.r, t[i__3].i = t11.i;

        if (wantq) {

/*           Accumulate transformation in the matrix Q. */

            d_cnjg(&z__1, &sn);
            zrot_(n, &q[k * q_dim1 + 1], &c__1, &q[(k + 1) * q_dim1 + 1], &
                    c__1, &cs, &z__1);
        }

/* L10: */
    }

    return 0;

/*     End of ZTREXC */

} /* ztrexc_ */