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## org.netlib.lapack
Class Dstegr

    java.lang.Object
      org.netlib.lapack.Dstegr

    public class Dstegr

extends java.lang.Object

    Following is the description from the original
    Fortran source.  For each array argument, the Java
    version will include an integer offset parameter, so
    the arguments may not match the description exactly.
    Contact seymour@cs.utk.edu with any questions.

     *     ..
     *
     *  Purpose
     *  =======
     *
     *  DSTEGR computes selected eigenvalues and, optionally, eigenvectors
     *  of a real symmetric tridiagonal matrix T. Any such unreduced matrix h
     *  a well defined set of pairwise different real eigenvalues, the corres
     *  real eigenvectors are pairwise orthogonal.
     *
     *  The spectrum may be computed either completely or partially by specif
     *  either an interval (VL,VU] or a range of indices IL:IU for the desire
     *  eigenvalues.
     *
     *  DSTEGR is a compatability wrapper around the improved DSTEMR routine.
     *  See DSTEMR for further details.
     *
     *  One important change is that the ABSTOL parameter no longer provides
     *  benefit and hence is no longer used.
     *
     *  Note : DSTEGR and DSTEMR 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) DOUBLE PRECISION array, dimension (N)
     *          On entry, the N diagonal elements of the tridiagonal matrix
     *          T. On exit, D is overwritten.
     *
     *  E       (input/output) DOUBLE PRECISION 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) DOUBLE PRECISION
     *  VU      (input) DOUBLE PRECISION
     *          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) DOUBLE PRECISION
     *          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) DOUBLE PRECISION array, dimension (N)
     *          The first M elements contain the selected eigenvalues in
     *          ascending order.
     *
     *  Z       (output) DOUBLE PRECISION 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 eigen
     *          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) DOUBLE PRECISION 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 DLARRE,
     *                if INFO = 2X, internal error in DLARRV.
     *                Here, the digit X = ABS( IINFO ) < 10, where IINFO is
     *                the nonzero error code returned by DLARRE or
     *                DLARRV, respectively.
     *
     *  Further Details
     *  ===============
     *
     *  Based on contributions by
     *     Inderjit Dhillon, IBM Almaden, USA
     *     Osni Marques, LBNL/NERSC, USA
     *     Christof Voemel, LBNL/NERSC, USA
     *
     *  =====================================================================
     *
     *     .. Local Scalars ..

Constructor Summary
`Dstegr()`

Method Summary
`static void` | `dstegr(java.lang.String jobz, java.lang.String range, int n, double[] d, int _d_offset, double[] e, int _e_offset, double vl, double vu, int il, int iu, double abstol, intW m, double[] w, int _w_offset, double[] z, int _z_offset, int ldz, int[] isuppz, int _isuppz_offset, double[] work, int _work_offset, int lwork, int[] iwork, int _iwork_offset, int liwork, intW info)`

Methods inherited from class java.lang.Object
`clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait`

Constructor Detail

### Dstegr

    public Dstegr()

Method Detail

### dstegr

    public static void dstegr(java.lang.String jobz,
                              java.lang.String range,
                              int n,
                              double[] d,
                              int _d_offset,
                              double[] e,
                              int _e_offset,
                              double vl,
                              double vu,
                              int il,
                              int iu,
                              double abstol,
                              intW m,
                              double[] w,
                              int _w_offset,
                              double[] z,
                              int _z_offset,
                              int ldz,
                              int[] isuppz,
                              int _isuppz_offset,
                              double[] work,
                              int _work_offset,
                              int lwork,
                              int[] iwork,
                              int _iwork_offset,
                              int liwork,
                              intW info)

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