strsna.c

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/* strsna.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;
static logical c_true = TRUE_;
static logical c_false = FALSE_;

/* Subroutine */ int strsna_(char *job, char *howmny, logical *select, 
        integer *n, real *t, integer *ldt, real *vl, integer *ldvl, real *vr, 
        integer *ldvr, real *s, real *sep, integer *mm, integer *m, real *
        work, integer *ldwork, integer *iwork, integer *info)
{
    /* System generated locals */
    integer t_dim1, t_offset, vl_dim1, vl_offset, vr_dim1, vr_offset, 
            work_dim1, work_offset, i__1, i__2;
    real r__1, r__2;

    /* Builtin functions */
    double sqrt(doublereal);

    /* Local variables */
    integer i__, j, k, n2;
    real cs;
    integer nn, ks;
    real sn, mu, eps, est;
    integer kase;
    real cond;
    logical pair;
    integer ierr;
    real dumm, prod;
    integer ifst;
    real lnrm;
    extern doublereal sdot_(integer *, real *, integer *, real *, integer *);
    integer ilst;
    real rnrm, prod1, prod2;
    extern doublereal snrm2_(integer *, real *, integer *);
    real scale, delta;
    extern logical lsame_(char *, char *);
    integer isave[3];
    logical wants;
    real dummy[1];
    extern /* Subroutine */ int slacn2_(integer *, real *, real *, integer *, 
            real *, integer *, integer *);
    extern doublereal slapy2_(real *, real *);
    extern /* Subroutine */ int slabad_(real *, real *);
    extern doublereal slamch_(char *);
    extern /* Subroutine */ int xerbla_(char *, integer *);
    real bignum;
    logical wantbh;
    extern /* Subroutine */ int slacpy_(char *, integer *, integer *, real *, 
            integer *, real *, integer *);
    logical somcon;
    extern /* Subroutine */ int slaqtr_(logical *, logical *, integer *, real 
            *, integer *, real *, real *, real *, real *, real *, integer *), 
            strexc_(char *, integer *, real *, integer *, real *, integer *, 
            integer *, integer *, real *, integer *);
    real smlnum;
    logical wantsp;


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

/*     Modified to call SLACN2 in place of SLACON, 7 Feb 03, SJH. */

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

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

/*  STRSNA estimates reciprocal condition numbers for specified */
/*  eigenvalues and/or right eigenvectors of a real upper */
/*  quasi-triangular matrix T (or of any matrix Q*T*Q**T with Q */
/*  orthogonal). */

/*  T must be in Schur canonical form (as returned by SHSEQR), that is, */
/*  block upper triangular with 1-by-1 and 2-by-2 diagonal blocks; each */
/*  2-by-2 diagonal block has its diagonal elements equal and its */
/*  off-diagonal elements of opposite sign. */

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

/*  JOB     (input) CHARACTER*1 */
/*          Specifies whether condition numbers are required for */
/*          eigenvalues (S) or eigenvectors (SEP): */
/*          = 'E': for eigenvalues only (S); */
/*          = 'V': for eigenvectors only (SEP); */
/*          = 'B': for both eigenvalues and eigenvectors (S and SEP). */

/*  HOWMNY  (input) CHARACTER*1 */
/*          = 'A': compute condition numbers for all eigenpairs; */
/*          = 'S': compute condition numbers for selected eigenpairs */
/*                 specified by the array SELECT. */

/*  SELECT  (input) LOGICAL array, dimension (N) */
/*          If HOWMNY = 'S', SELECT specifies the eigenpairs for which */
/*          condition numbers are required. To select condition numbers */
/*          for the eigenpair corresponding to a real eigenvalue w(j), */
/*          SELECT(j) must be set to .TRUE.. To select condition numbers */
/*          corresponding to a complex conjugate pair of eigenvalues w(j) */
/*          and w(j+1), either SELECT(j) or SELECT(j+1) or both, must be */
/*          set to .TRUE.. */
/*          If HOWMNY = 'A', SELECT is not referenced. */

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

/*  T       (input) REAL array, dimension (LDT,N) */
/*          The upper quasi-triangular matrix T, in Schur canonical form. */

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

/*  VL      (input) REAL array, dimension (LDVL,M) */
/*          If JOB = 'E' or 'B', VL must contain left eigenvectors of T */
/*          (or of any Q*T*Q**T with Q orthogonal), corresponding to the */
/*          eigenpairs specified by HOWMNY and SELECT. The eigenvectors */
/*          must be stored in consecutive columns of VL, as returned by */
/*          SHSEIN or STREVC. */
/*          If JOB = 'V', VL is not referenced. */

/*  LDVL    (input) INTEGER */
/*          The leading dimension of the array VL. */
/*          LDVL >= 1; and if JOB = 'E' or 'B', LDVL >= N. */

/*  VR      (input) REAL array, dimension (LDVR,M) */
/*          If JOB = 'E' or 'B', VR must contain right eigenvectors of T */
/*          (or of any Q*T*Q**T with Q orthogonal), corresponding to the */
/*          eigenpairs specified by HOWMNY and SELECT. The eigenvectors */
/*          must be stored in consecutive columns of VR, as returned by */
/*          SHSEIN or STREVC. */
/*          If JOB = 'V', VR is not referenced. */

/*  LDVR    (input) INTEGER */
/*          The leading dimension of the array VR. */
/*          LDVR >= 1; and if JOB = 'E' or 'B', LDVR >= N. */

/*  S       (output) REAL array, dimension (MM) */
/*          If JOB = 'E' or 'B', the reciprocal condition numbers of the */
/*          selected eigenvalues, stored in consecutive elements of the */
/*          array. For a complex conjugate pair of eigenvalues two */
/*          consecutive elements of S are set to the same value. Thus */
/*          S(j), SEP(j), and the j-th columns of VL and VR all */
/*          correspond to the same eigenpair (but not in general the */
/*          j-th eigenpair, unless all eigenpairs are selected). */
/*          If JOB = 'V', S is not referenced. */

/*  SEP     (output) REAL array, dimension (MM) */
/*          If JOB = 'V' or 'B', the estimated reciprocal condition */
/*          numbers of the selected eigenvectors, stored in consecutive */
/*          elements of the array. For a complex eigenvector two */
/*          consecutive elements of SEP are set to the same value. If */
/*          the eigenvalues cannot be reordered to compute SEP(j), SEP(j) */
/*          is set to 0; this can only occur when the true value would be */
/*          very small anyway. */
/*          If JOB = 'E', SEP is not referenced. */

/*  MM      (input) INTEGER */
/*          The number of elements in the arrays S (if JOB = 'E' or 'B') */
/*           and/or SEP (if JOB = 'V' or 'B'). MM >= M. */

/*  M       (output) INTEGER */
/*          The number of elements of the arrays S and/or SEP actually */
/*          used to store the estimated condition numbers. */
/*          If HOWMNY = 'A', M is set to N. */

/*  WORK    (workspace) REAL array, dimension (LDWORK,N+6) */
/*          If JOB = 'E', WORK is not referenced. */

/*  LDWORK  (input) INTEGER */
/*          The leading dimension of the array WORK. */
/*          LDWORK >= 1; and if JOB = 'V' or 'B', LDWORK >= N. */

/*  IWORK   (workspace) INTEGER array, dimension (2*(N-1)) */
/*          If JOB = 'E', IWORK is not referenced. */

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

/*  Further Details */
/*  =============== */

/*  The reciprocal of the condition number of an eigenvalue lambda is */
/*  defined as */

/*          S(lambda) = |v'*u| / (norm(u)*norm(v)) */

/*  where u and v are the right and left eigenvectors of T corresponding */
/*  to lambda; v' denotes the conjugate-transpose of v, and norm(u) */
/*  denotes the Euclidean norm. These reciprocal condition numbers always */
/*  lie between zero (very badly conditioned) and one (very well */
/*  conditioned). If n = 1, S(lambda) is defined to be 1. */

/*  An approximate error bound for a computed eigenvalue W(i) is given by */

/*                      EPS * norm(T) / S(i) */

/*  where EPS is the machine precision. */

/*  The reciprocal of the condition number of the right eigenvector u */
/*  corresponding to lambda is defined as follows. Suppose */

/*              T = ( lambda  c  ) */
/*                  (   0    T22 ) */

/*  Then the reciprocal condition number is */

/*          SEP( lambda, T22 ) = sigma-min( T22 - lambda*I ) */

/*  where sigma-min denotes the smallest singular value. We approximate */
/*  the smallest singular value by the reciprocal of an estimate of the */
/*  one-norm of the inverse of T22 - lambda*I. If n = 1, SEP(1) is */
/*  defined to be abs(T(1,1)). */

/*  An approximate error bound for a computed right eigenvector VR(i) */
/*  is given by */

/*                      EPS * norm(T) / SEP(i) */

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

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

/*     Decode and test the input parameters */

    /* Parameter adjustments */
    --select;
    t_dim1 = *ldt;
    t_offset = 1 + t_dim1;
    t -= t_offset;
    vl_dim1 = *ldvl;
    vl_offset = 1 + vl_dim1;
    vl -= vl_offset;
    vr_dim1 = *ldvr;
    vr_offset = 1 + vr_dim1;
    vr -= vr_offset;
    --s;
    --sep;
    work_dim1 = *ldwork;
    work_offset = 1 + work_dim1;
    work -= work_offset;
    --iwork;

    /* Function Body */
    wantbh = lsame_(job, "B");
    wants = lsame_(job, "E") || wantbh;
    wantsp = lsame_(job, "V") || wantbh;

    somcon = lsame_(howmny, "S");

    *info = 0;
    if (! wants && ! wantsp) {
        *info = -1;
    } else if (! lsame_(howmny, "A") && ! somcon) {
        *info = -2;
    } else if (*n < 0) {
        *info = -4;
    } else if (*ldt < max(1,*n)) {
        *info = -6;
    } else if (*ldvl < 1 || wants && *ldvl < *n) {
        *info = -8;
    } else if (*ldvr < 1 || wants && *ldvr < *n) {
        *info = -10;
    } else {

/*        Set M to the number of eigenpairs for which condition numbers */
/*        are required, and test MM. */

        if (somcon) {
            *m = 0;
            pair = FALSE_;
            i__1 = *n;
            for (k = 1; k <= i__1; ++k) {
                if (pair) {
                    pair = FALSE_;
                } else {
                    if (k < *n) {
                        if (t[k + 1 + k * t_dim1] == 0.f) {
                            if (select[k]) {
                                ++(*m);
                            }
                        } else {
                            pair = TRUE_;
                            if (select[k] || select[k + 1]) {
                                *m += 2;
                            }
                        }
                    } else {
                        if (select[*n]) {
                            ++(*m);
                        }
                    }
                }
/* L10: */
            }
        } else {
            *m = *n;
        }

        if (*mm < *m) {
            *info = -13;
        } else if (*ldwork < 1 || wantsp && *ldwork < *n) {
            *info = -16;
        }
    }
    if (*info != 0) {
        i__1 = -(*info);
        xerbla_("STRSNA", &i__1);
        return 0;
    }

/*     Quick return if possible */

    if (*n == 0) {
        return 0;
    }

    if (*n == 1) {
        if (somcon) {
            if (! select[1]) {
                return 0;
            }
        }
        if (wants) {
            s[1] = 1.f;
        }
        if (wantsp) {
            sep[1] = (r__1 = t[t_dim1 + 1], dabs(r__1));
        }
        return 0;
    }

/*     Get machine constants */

    eps = slamch_("P");
    smlnum = slamch_("S") / eps;
    bignum = 1.f / smlnum;
    slabad_(&smlnum, &bignum);

    ks = 0;
    pair = FALSE_;
    i__1 = *n;
    for (k = 1; k <= i__1; ++k) {

/*        Determine whether T(k,k) begins a 1-by-1 or 2-by-2 block. */

        if (pair) {
            pair = FALSE_;
            goto L60;
        } else {
            if (k < *n) {
                pair = t[k + 1 + k * t_dim1] != 0.f;
            }
        }

/*        Determine whether condition numbers are required for the k-th */
/*        eigenpair. */

        if (somcon) {
            if (pair) {
                if (! select[k] && ! select[k + 1]) {
                    goto L60;
                }
            } else {
                if (! select[k]) {
                    goto L60;
                }
            }
        }

        ++ks;

        if (wants) {

/*           Compute the reciprocal condition number of the k-th */
/*           eigenvalue. */

            if (! pair) {

/*              Real eigenvalue. */

                prod = sdot_(n, &vr[ks * vr_dim1 + 1], &c__1, &vl[ks * 
                        vl_dim1 + 1], &c__1);
                rnrm = snrm2_(n, &vr[ks * vr_dim1 + 1], &c__1);
                lnrm = snrm2_(n, &vl[ks * vl_dim1 + 1], &c__1);
                s[ks] = dabs(prod) / (rnrm * lnrm);
            } else {

/*              Complex eigenvalue. */

                prod1 = sdot_(n, &vr[ks * vr_dim1 + 1], &c__1, &vl[ks * 
                        vl_dim1 + 1], &c__1);
                prod1 += sdot_(n, &vr[(ks + 1) * vr_dim1 + 1], &c__1, &vl[(ks 
                        + 1) * vl_dim1 + 1], &c__1);
                prod2 = sdot_(n, &vl[ks * vl_dim1 + 1], &c__1, &vr[(ks + 1) * 
                        vr_dim1 + 1], &c__1);
                prod2 -= sdot_(n, &vl[(ks + 1) * vl_dim1 + 1], &c__1, &vr[ks *
                         vr_dim1 + 1], &c__1);
                r__1 = snrm2_(n, &vr[ks * vr_dim1 + 1], &c__1);
                r__2 = snrm2_(n, &vr[(ks + 1) * vr_dim1 + 1], &c__1);
                rnrm = slapy2_(&r__1, &r__2);
                r__1 = snrm2_(n, &vl[ks * vl_dim1 + 1], &c__1);
                r__2 = snrm2_(n, &vl[(ks + 1) * vl_dim1 + 1], &c__1);
                lnrm = slapy2_(&r__1, &r__2);
                cond = slapy2_(&prod1, &prod2) / (rnrm * lnrm);
                s[ks] = cond;
                s[ks + 1] = cond;
            }
        }

        if (wantsp) {

/*           Estimate the reciprocal condition number of the k-th */
/*           eigenvector. */

/*           Copy the matrix T to the array WORK and swap the diagonal */
/*           block beginning at T(k,k) to the (1,1) position. */

            slacpy_("Full", n, n, &t[t_offset], ldt, &work[work_offset], 
                    ldwork);
            ifst = k;
            ilst = 1;
            strexc_("No Q", n, &work[work_offset], ldwork, dummy, &c__1, &
                    ifst, &ilst, &work[(*n + 1) * work_dim1 + 1], &ierr);

            if (ierr == 1 || ierr == 2) {

/*              Could not swap because blocks not well separated */

                scale = 1.f;
                est = bignum;
            } else {

/*              Reordering successful */

                if (work[work_dim1 + 2] == 0.f) {

/*                 Form C = T22 - lambda*I in WORK(2:N,2:N). */

                    i__2 = *n;
                    for (i__ = 2; i__ <= i__2; ++i__) {
                        work[i__ + i__ * work_dim1] -= work[work_dim1 + 1];
/* L20: */
                    }
                    n2 = 1;
                    nn = *n - 1;
                } else {

/*                 Triangularize the 2 by 2 block by unitary */
/*                 transformation U = [  cs   i*ss ] */
/*                                    [ i*ss   cs  ]. */
/*                 such that the (1,1) position of WORK is complex */
/*                 eigenvalue lambda with positive imaginary part. (2,2) */
/*                 position of WORK is the complex eigenvalue lambda */
/*                 with negative imaginary  part. */

                    mu = sqrt((r__1 = work[(work_dim1 << 1) + 1], dabs(r__1)))
                             * sqrt((r__2 = work[work_dim1 + 2], dabs(r__2)));
                    delta = slapy2_(&mu, &work[work_dim1 + 2]);
                    cs = mu / delta;
                    sn = -work[work_dim1 + 2] / delta;

/*                 Form */

/*                 C' = WORK(2:N,2:N) + i*[rwork(1) ..... rwork(n-1) ] */
/*                                        [   mu                     ] */
/*                                        [         ..               ] */
/*                                        [             ..           ] */
/*                                        [                  mu      ] */
/*                 where C' is conjugate transpose of complex matrix C, */
/*                 and RWORK is stored starting in the N+1-st column of */
/*                 WORK. */

                    i__2 = *n;
                    for (j = 3; j <= i__2; ++j) {
                        work[j * work_dim1 + 2] = cs * work[j * work_dim1 + 2]
                                ;
                        work[j + j * work_dim1] -= work[work_dim1 + 1];
/* L30: */
                    }
                    work[(work_dim1 << 1) + 2] = 0.f;

                    work[(*n + 1) * work_dim1 + 1] = mu * 2.f;
                    i__2 = *n - 1;
                    for (i__ = 2; i__ <= i__2; ++i__) {
                        work[i__ + (*n + 1) * work_dim1] = sn * work[(i__ + 1)
                                 * work_dim1 + 1];
/* L40: */
                    }
                    n2 = 2;
                    nn = *n - 1 << 1;
                }

/*              Estimate norm(inv(C')) */

                est = 0.f;
                kase = 0;
L50:
                slacn2_(&nn, &work[(*n + 2) * work_dim1 + 1], &work[(*n + 4) *
                         work_dim1 + 1], &iwork[1], &est, &kase, isave);
                if (kase != 0) {
                    if (kase == 1) {
                        if (n2 == 1) {

/*                       Real eigenvalue: solve C'*x = scale*c. */

                            i__2 = *n - 1;
                            slaqtr_(&c_true, &c_true, &i__2, &work[(work_dim1 
                                    << 1) + 2], ldwork, dummy, &dumm, &scale, 
                                    &work[(*n + 4) * work_dim1 + 1], &work[(*
                                    n + 6) * work_dim1 + 1], &ierr);
                        } else {

/*                       Complex eigenvalue: solve */
/*                       C'*(p+iq) = scale*(c+id) in real arithmetic. */

                            i__2 = *n - 1;
                            slaqtr_(&c_true, &c_false, &i__2, &work[(
                                    work_dim1 << 1) + 2], ldwork, &work[(*n + 
                                    1) * work_dim1 + 1], &mu, &scale, &work[(*
                                    n + 4) * work_dim1 + 1], &work[(*n + 6) * 
                                    work_dim1 + 1], &ierr);
                        }
                    } else {
                        if (n2 == 1) {

/*                       Real eigenvalue: solve C*x = scale*c. */

                            i__2 = *n - 1;
                            slaqtr_(&c_false, &c_true, &i__2, &work[(
                                    work_dim1 << 1) + 2], ldwork, dummy, &
                                    dumm, &scale, &work[(*n + 4) * work_dim1 
                                    + 1], &work[(*n + 6) * work_dim1 + 1], &
                                    ierr);
                        } else {

/*                       Complex eigenvalue: solve */
/*                       C*(p+iq) = scale*(c+id) in real arithmetic. */

                            i__2 = *n - 1;
                            slaqtr_(&c_false, &c_false, &i__2, &work[(
                                    work_dim1 << 1) + 2], ldwork, &work[(*n + 
                                    1) * work_dim1 + 1], &mu, &scale, &work[(*
                                    n + 4) * work_dim1 + 1], &work[(*n + 6) * 
                                    work_dim1 + 1], &ierr);

                        }
                    }

                    goto L50;
                }
            }

            sep[ks] = scale / dmax(est,smlnum);
            if (pair) {
                sep[ks + 1] = sep[ks];
            }
        }

        if (pair) {
            ++ks;
        }

L60:
        ;
    }
    return 0;

/*     End of STRSNA */

} /* strsna_ */