sgebak.c

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/* sgebak.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"

/* Subroutine */ int sgebak_(char *job, char *side, integer *n, integer *ilo, 
        integer *ihi, real *scale, integer *m, real *v, integer *ldv, integer 
        *info)
{
    /* System generated locals */
    integer v_dim1, v_offset, i__1;

    /* Local variables */
    integer i__, k;
    real s;
    integer ii;
    extern logical lsame_(char *, char *);
    extern /* Subroutine */ int sscal_(integer *, real *, real *, integer *);
    logical leftv;
    extern /* Subroutine */ int sswap_(integer *, real *, integer *, real *, 
            integer *), xerbla_(char *, integer *);
    logical rightv;


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

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

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

/*  SGEBAK forms the right or left eigenvectors of a real general matrix */
/*  by backward transformation on the computed eigenvectors of the */
/*  balanced matrix output by SGEBAL. */

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

/*  JOB     (input) CHARACTER*1 */
/*          Specifies the type of backward transformation required: */
/*          = 'N', do nothing, return immediately; */
/*          = 'P', do backward transformation for permutation only; */
/*          = 'S', do backward transformation for scaling only; */
/*          = 'B', do backward transformations for both permutation and */
/*                 scaling. */
/*          JOB must be the same as the argument JOB supplied to SGEBAL. */

/*  SIDE    (input) CHARACTER*1 */
/*          = 'R':  V contains right eigenvectors; */
/*          = 'L':  V contains left eigenvectors. */

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

/*  ILO     (input) INTEGER */
/*  IHI     (input) INTEGER */
/*          The integers ILO and IHI determined by SGEBAL. */
/*          1 <= ILO <= IHI <= N, if N > 0; ILO=1 and IHI=0, if N=0. */

/*  SCALE   (input) REAL array, dimension (N) */
/*          Details of the permutation and scaling factors, as returned */
/*          by SGEBAL. */

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

/*  V       (input/output) REAL array, dimension (LDV,M) */
/*          On entry, the matrix of right or left eigenvectors to be */
/*          transformed, as returned by SHSEIN or STREVC. */
/*          On exit, V is overwritten by the transformed eigenvectors. */

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

/*  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 .. */

/*     Decode and Test the input parameters */

    /* Parameter adjustments */
    --scale;
    v_dim1 = *ldv;
    v_offset = 1 + v_dim1;
    v -= v_offset;

    /* Function Body */
    rightv = lsame_(side, "R");
    leftv = lsame_(side, "L");

    *info = 0;
    if (! lsame_(job, "N") && ! lsame_(job, "P") && ! lsame_(job, "S") 
            && ! lsame_(job, "B")) {
        *info = -1;
    } else if (! rightv && ! leftv) {
        *info = -2;
    } else if (*n < 0) {
        *info = -3;
    } else if (*ilo < 1 || *ilo > max(1,*n)) {
        *info = -4;
    } else if (*ihi < min(*ilo,*n) || *ihi > *n) {
        *info = -5;
    } else if (*m < 0) {
        *info = -7;
    } else if (*ldv < max(1,*n)) {
        *info = -9;
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("SGEBAK", &i__1);
        return 0;
    }

/*     Quick return if possible */

    if (*n == 0) {
        return 0;
    }
    if (*m == 0) {
        return 0;
    }
    if (lsame_(job, "N")) {
        return 0;
    }

    if (*ilo == *ihi) {
        goto L30;
    }

/*     Backward balance */

    if (lsame_(job, "S") || lsame_(job, "B")) {

        if (rightv) {
            i__1 = *ihi;
            for (i__ = *ilo; i__ <= i__1; ++i__) {
                s = scale[i__];
                sscal_(m, &s, &v[i__ + v_dim1], ldv);
/* L10: */
            }
        }

        if (leftv) {
            i__1 = *ihi;
            for (i__ = *ilo; i__ <= i__1; ++i__) {
                s = 1.f / scale[i__];
                sscal_(m, &s, &v[i__ + v_dim1], ldv);
/* L20: */
            }
        }

    }

/*     Backward permutation */

/*     For  I = ILO-1 step -1 until 1, */
/*              IHI+1 step 1 until N do -- */

L30:
    if (lsame_(job, "P") || lsame_(job, "B")) {
        if (rightv) {
            i__1 = *n;
            for (ii = 1; ii <= i__1; ++ii) {
                i__ = ii;
                if (i__ >= *ilo && i__ <= *ihi) {
                    goto L40;
                }
                if (i__ < *ilo) {
                    i__ = *ilo - ii;
                }
                k = scale[i__];
                if (k == i__) {
                    goto L40;
                }
                sswap_(m, &v[i__ + v_dim1], ldv, &v[k + v_dim1], ldv);
L40:
                ;
            }
        }

        if (leftv) {
            i__1 = *n;
            for (ii = 1; ii <= i__1; ++ii) {
                i__ = ii;
                if (i__ >= *ilo && i__ <= *ihi) {
                    goto L50;
                }
                if (i__ < *ilo) {
                    i__ = *ilo - ii;
                }
                k = scale[i__];
                if (k == i__) {
                    goto L50;
                }
                sswap_(m, &v[i__ + v_dim1], ldv, &v[k + v_dim1], ldv);
L50:
                ;
            }
        }
    }

    return 0;

/*     End of SGEBAK */

} /* sgebak_ */