org.netlib.lapack
Class Dlarre

java.lang.Object
  org.netlib.lapack.Dlarre

public class Dlarre
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
 *  =======
 *
 *  Given the tridiagonal matrix T, DLARRE sets "small" off-diagonal
 *  elements to zero, and for each unreduced block T_i, it finds
 *  (i) the numbers sigma_i
 *  (ii) the base T_i - sigma_i I = L_i D_i L_i^T representations and
 *  (iii) eigenvalues of each L_i D_i L_i^T.
 *  The representations and eigenvalues found are then used by
 *  DSTEGR to compute the eigenvectors of a symmetric tridiagonal
 *  matrix. Currently, the base representations are limited to being
 *  positive or negative definite, and the eigenvalues of the definite
 *  matrices are found by the dqds algorithm (subroutine DLASQ2). As
 *  an added benefit, DLARRE also outputs the n Gerschgorin
 *  intervals for each L_i D_i L_i^T.
 *
 *  Arguments
 *  =========
 *
 *  N       (input) INTEGER
 *          The order of the matrix.
 *
 *  D       (input/output) DOUBLE PRECISION array, dimension (N)
 *          On entry, the n diagonal elements of the tridiagonal
 *          matrix T.
 *          On exit, the n diagonal elements of the diagonal
 *          matrices D_i.
 *
 *  E       (input/output) DOUBLE PRECISION array, dimension (N)
 *          On entry, the (n-1) subdiagonal elements of the tridiagonal
 *          matrix T; E(N) need not be set.
 *          On exit, the subdiagonal elements of the unit bidiagonal
 *          matrices L_i.
 *
 *  TOL     (input) DOUBLE PRECISION
 *          The threshold for splitting. If on input |E(i)| < TOL, then
 *          the matrix T is split into smaller blocks.
 *
 *  NSPLIT  (input) INTEGER
 *          The number of blocks T splits into. 1 <= NSPLIT <= N.
 *
 *  ISPLIT  (output) INTEGER array, dimension (2*N)
 *          The splitting points, at which T breaks up into submatrices.

 *          The first submatrix consists of rows/columns 1 to ISPLIT(1),

 *          the second of rows/columns ISPLIT(1)+1 through ISPLIT(2),
 *          etc., and the NSPLIT-th consists of rows/columns
 *          ISPLIT(NSPLIT-1)+1 through ISPLIT(NSPLIT)=N.
 *
 *  M       (output) INTEGER
 *          The total number of eigenvalues (of all the L_i D_i L_i^T)
 *          found.
 *
 *  W       (output) DOUBLE PRECISION array, dimension (N)
 *          The first M elements contain the eigenvalues. The
 *          eigenvalues of each of the blocks, L_i D_i L_i^T, are
 *          sorted in ascending order.
 *
 *  WOFF    (output) DOUBLE PRECISION array, dimension (N)
 *          The NSPLIT base points sigma_i.
 *
 *  GERSCH  (output) DOUBLE PRECISION array, dimension (2*N)
 *          The n Gerschgorin intervals.
 *
 *  WORK    (input) DOUBLE PRECISION array, dimension (4*N???)
 *          Workspace.
 *
 *  INFO    (output) INTEGER
 *          Output error code from DLASQ2
 *
 *  Further Details
 *  ===============
 *
 *  Based on contributions by
 *     Inderjit Dhillon, IBM Almaden, USA
 *     Osni Marques, LBNL/NERSC, USA
 *
 *  =====================================================================
 *
 *     .. Parameters ..

Constructor Summary

Dlarre()

Method Summary

static void

dlarre(int n, double[] d, int _d_offset, double[] e, int _e_offset, double tol, intW nsplit, int[] isplit, int _isplit_offset, intW m, double[] w, int _w_offset, double[] woff, int _woff_offset, double[] gersch, int _gersch_offset, double[] work, int _work_offset, intW info)

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Dlarre

public Dlarre()

Method Detail

dlarre

public static void dlarre(int n,
                          double[] d,
                          int _d_offset,
                          double[] e,
                          int _e_offset,
                          double tol,
                          intW nsplit,
                          int[] isplit,
                          int _isplit_offset,
                          intW m,
                          double[] w,
                          int _w_offset,
                          double[] woff,
                          int _woff_offset,
                          double[] gersch,
                          int _gersch_offset,
                          double[] work,
                          int _work_offset,
                          intW info)