sstegr.c

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/* sstegr.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 sstegr_(char *jobz, char *range, integer *n, real *d__, 
        real *e, real *vl, real *vu, integer *il, integer *iu, real *abstol, 
        integer *m, real *w, real *z__, integer *ldz, integer *isuppz, real *
        work, integer *lwork, integer *iwork, integer *liwork, integer *info)
{
    /* System generated locals */
    integer z_dim1, z_offset;

    /* Local variables */
    logical tryrac;
    extern /* Subroutine */ int sstemr_(char *, char *, integer *, real *, 
            real *, real *, real *, integer *, integer *, integer *, real *, 
            real *, integer *, integer *, integer *, logical *, real *, 
            integer *, integer *, integer *, integer *);



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

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

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

/*  SSTEGR computes selected eigenvalues and, optionally, eigenvectors */
/*  of a real symmetric tridiagonal matrix T. Any such unreduced matrix has */
/*  a well defined set of pairwise different real eigenvalues, the corresponding */
/*  real eigenvectors are pairwise orthogonal. */

/*  The spectrum may be computed either completely or partially by specifying */
/*  either an interval (VL,VU] or a range of indices IL:IU for the desired */
/*  eigenvalues. */

/*  SSTEGR is a compatability wrapper around the improved SSTEMR routine. */
/*  See SSTEMR for further details. */

/*  One important change is that the ABSTOL parameter no longer provides any */
/*  benefit and hence is no longer used. */

/*  Note : SSTEGR and SSTEMR work only on machines which follow */
/*  IEEE-754 floating-point standard in their handling of infinities and */
/*  NaNs.  Normal execution may create these exceptiona values and hence */
/*  may abort due to a floating point exception in environments which */
/*  do not conform to the IEEE-754 standard. */

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

/*  JOBZ    (input) CHARACTER*1 */
/*          = 'N':  Compute eigenvalues only; */
/*          = 'V':  Compute eigenvalues and eigenvectors. */

/*  RANGE   (input) CHARACTER*1 */
/*          = 'A': all eigenvalues will be found. */
/*          = 'V': all eigenvalues in the half-open interval (VL,VU] */
/*                 will be found. */
/*          = 'I': the IL-th through IU-th eigenvalues will be found. */

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

/*  D       (input/output) REAL array, dimension (N) */
/*          On entry, the N diagonal elements of the tridiagonal matrix */
/*          T. On exit, D is overwritten. */

/*  E       (input/output) REAL array, dimension (N) */
/*          On entry, the (N-1) subdiagonal elements of the tridiagonal */
/*          matrix T in elements 1 to N-1 of E. E(N) need not be set on */
/*          input, but is used internally as workspace. */
/*          On exit, E is overwritten. */

/*  VL      (input) REAL */
/*  VU      (input) REAL */
/*          If RANGE='V', the lower and upper bounds of the interval to */
/*          be searched for eigenvalues. VL < VU. */
/*          Not referenced if RANGE = 'A' or 'I'. */

/*  IL      (input) INTEGER */
/*  IU      (input) INTEGER */
/*          If RANGE='I', the indices (in ascending order) of the */
/*          smallest and largest eigenvalues to be returned. */
/*          1 <= IL <= IU <= N, if N > 0. */
/*          Not referenced if RANGE = 'A' or 'V'. */

/*  ABSTOL  (input) REAL */
/*          Unused.  Was the absolute error tolerance for the */
/*          eigenvalues/eigenvectors in previous versions. */

/*  M       (output) INTEGER */
/*          The total number of eigenvalues found.  0 <= M <= N. */
/*          If RANGE = 'A', M = N, and if RANGE = 'I', M = IU-IL+1. */

/*  W       (output) REAL array, dimension (N) */
/*          The first M elements contain the selected eigenvalues in */
/*          ascending order. */

/*  Z       (output) REAL array, dimension (LDZ, max(1,M) ) */
/*          If JOBZ = 'V', and if INFO = 0, then the first M columns of Z */
/*          contain the orthonormal eigenvectors of the matrix T */
/*          corresponding to the selected eigenvalues, with the i-th */
/*          column of Z holding the eigenvector associated with W(i). */
/*          If JOBZ = 'N', then Z is not referenced. */
/*          Note: the user must ensure that at least max(1,M) columns are */
/*          supplied in the array Z; if RANGE = 'V', the exact value of M */
/*          is not known in advance and an upper bound must be used. */
/*          Supplying N columns is always safe. */

/*  LDZ     (input) INTEGER */
/*          The leading dimension of the array Z.  LDZ >= 1, and if */
/*          JOBZ = 'V', then LDZ >= max(1,N). */

/*  ISUPPZ  (output) INTEGER ARRAY, dimension ( 2*max(1,M) ) */
/*          The support of the eigenvectors in Z, i.e., the indices */
/*          indicating the nonzero elements in Z. The i-th computed eigenvector */
/*          is nonzero only in elements ISUPPZ( 2*i-1 ) through */
/*          ISUPPZ( 2*i ). This is relevant in the case when the matrix */
/*          is split. ISUPPZ is only accessed when JOBZ is 'V' and N > 0. */

/*  WORK    (workspace/output) REAL array, dimension (LWORK) */
/*          On exit, if INFO = 0, WORK(1) returns the optimal */
/*          (and minimal) LWORK. */

/*  LWORK   (input) INTEGER */
/*          The dimension of the array WORK. LWORK >= max(1,18*N) */
/*          if JOBZ = 'V', and LWORK >= max(1,12*N) if JOBZ = 'N'. */
/*          If LWORK = -1, then a workspace query is assumed; the routine */
/*          only calculates the optimal size of the WORK array, returns */
/*          this value as the first entry of the WORK array, and no error */
/*          message related to LWORK is issued by XERBLA. */

/*  IWORK   (workspace/output) INTEGER array, dimension (LIWORK) */
/*          On exit, if INFO = 0, IWORK(1) returns the optimal LIWORK. */

/*  LIWORK  (input) INTEGER */
/*          The dimension of the array IWORK.  LIWORK >= max(1,10*N) */
/*          if the eigenvectors are desired, and LIWORK >= max(1,8*N) */
/*          if only the eigenvalues are to be computed. */
/*          If LIWORK = -1, then a workspace query is assumed; the */
/*          routine only calculates the optimal size of the IWORK array, */
/*          returns this value as the first entry of the IWORK array, and */
/*          no error message related to LIWORK is issued by XERBLA. */

/*  INFO    (output) INTEGER */
/*          On exit, INFO */
/*          = 0:  successful exit */
/*          < 0:  if INFO = -i, the i-th argument had an illegal value */
/*          > 0:  if INFO = 1X, internal error in SLARRE, */
/*                if INFO = 2X, internal error in SLARRV. */
/*                Here, the digit X = ABS( IINFO ) < 10, where IINFO is */
/*                the nonzero error code returned by SLARRE or */
/*                SLARRV, respectively. */

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

/*  Based on contributions by */
/*     Inderjit Dhillon, IBM Almaden, USA */
/*     Osni Marques, LBNL/NERSC, USA */
/*     Christof Voemel, LBNL/NERSC, USA */

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

/*     .. Local Scalars .. */
/*     .. */
/*     .. External Subroutines .. */
/*     .. */
/*     .. Executable Statements .. */
    /* Parameter adjustments */
    --d__;
    --e;
    --w;
    z_dim1 = *ldz;
    z_offset = 1 + z_dim1;
    z__ -= z_offset;
    --isuppz;
    --work;
    --iwork;

    /* Function Body */
    *info = 0;
    tryrac = FALSE_;
    sstemr_(jobz, range, n, &d__[1], &e[1], vl, vu, il, iu, m, &w[1], &z__[
            z_offset], ldz, n, &isuppz[1], &tryrac, &work[1], lwork, &iwork[1]
, liwork, info);

/*     End of SSTEGR */

    return 0;
} /* sstegr_ */