org.netlib.lapack
Class Dlahqr

java.lang.Object
  org.netlib.lapack.Dlahqr

public class Dlahqr
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
 *  =======
 *
 *  DLAHQR is an auxiliary routine called by DHSEQR to update the
 *  eigenvalues and Schur decomposition already computed by DHSEQR, by
 *  dealing with the Hessenberg submatrix in rows and columns ILO to IHI.
 *
 *  Arguments
 *  =========
 *
 *  WANTT   (input) LOGICAL
 *          = .TRUE. : the full Schur form T is required;
 *          = .FALSE.: only eigenvalues are required.
 *
 *  WANTZ   (input) LOGICAL
 *          = .TRUE. : the matrix of Schur vectors Z is required;
 *          = .FALSE.: Schur vectors are not required.
 *
 *  N       (input) INTEGER
 *          The order of the matrix H.  N >= 0.
 *
 *  ILO     (input) INTEGER
 *  IHI     (input) INTEGER
 *          It is assumed that H is already upper quasi-triangular in
 *          rows and columns IHI+1:N, and that H(ILO,ILO-1) = 0 (unless
 *          ILO = 1). DLAHQR works primarily with the Hessenberg
 *          submatrix in rows and columns ILO to IHI, but applies
 *          transformations to all of H if WANTT is .TRUE..
 *          1 <= ILO <= max(1,IHI); IHI <= N.
 *
 *  H       (input/output) DOUBLE PRECISION array, dimension (LDH,N)
 *          On entry, the upper Hessenberg matrix H.
 *          On exit, if WANTT is .TRUE., H is upper quasi-triangular in
 *          rows and columns ILO:IHI, with any 2-by-2 diagonal blocks in

 *          standard form. If WANTT is .FALSE., the contents of H are
 *          unspecified on exit.
 *
 *  LDH     (input) INTEGER
 *          The leading dimension of the array H. LDH >= max(1,N).
 *
 *  WR      (output) DOUBLE PRECISION array, dimension (N)
 *  WI      (output) DOUBLE PRECISION array, dimension (N)
 *          The real and imaginary parts, respectively, of the computed
 *          eigenvalues ILO to IHI are stored in the corresponding
 *          elements of WR and WI. If two eigenvalues are computed as a
 *          complex conjugate pair, they are stored in consecutive
 *          elements of WR and WI, say the i-th and (i+1)th, with
 *          WI(i) > 0 and WI(i+1) < 0. If WANTT is .TRUE., the
 *          eigenvalues are stored in the same order as on the diagonal
 *          of the Schur form returned in H, with WR(i) = H(i,i), and, if
 *          H(i:i+1,i:i+1) is a 2-by-2 diagonal block,
 *          WI(i) = sqrt(H(i+1,i)*H(i,i+1)) and WI(i+1) = -WI(i).
 *
 *  ILOZ    (input) INTEGER
 *  IHIZ    (input) INTEGER
 *          Specify the rows of Z to which transformations must be
 *          applied if WANTZ is .TRUE..
 *          1 <= ILOZ <= ILO; IHI <= IHIZ <= N.
 *
 *  Z       (input/output) DOUBLE PRECISION array, dimension (LDZ,N)
 *          If WANTZ is .TRUE., on entry Z must contain the current
 *          matrix Z of transformations accumulated by DHSEQR, and on
 *          exit Z has been updated; transformations are applied only to

 *          the submatrix Z(ILOZ:IHIZ,ILO:IHI).
 *          If WANTZ is .FALSE., Z is not referenced.
 *
 *  LDZ     (input) INTEGER
 *          The leading dimension of the array Z. LDZ >= max(1,N).
 *
 *  INFO    (output) INTEGER
 *          = 0: successful exit
 *          > 0: DLAHQR failed to compute all the eigenvalues ILO to IHI

 *               in a total of 30*(IHI-ILO+1) iterations; if INFO = i,
 *               elements i+1:ihi of WR and WI contain those eigenvalues

 *               which have been successfully computed.
 *
 *  Further Details
 *  ===============
 *
 *  2-96 Based on modifications by
 *     David Day, Sandia National Laboratory, USA
 *
 *  =====================================================================
 *
 *     .. Parameters ..

Constructor Summary

Dlahqr()

Method Summary

static void

dlahqr(boolean wantt, boolean wantz, int n, int ilo, int ihi, double[] h, int _h_offset, int ldh, double[] wr, int _wr_offset, double[] wi, int _wi_offset, int iloz, int ihiz, double[] z, int _z_offset, int ldz, intW info)

Methods inherited from class java.lang.Object

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

Constructor Detail

Dlahqr

public Dlahqr()

Method Detail

dlahqr

public static void dlahqr(boolean wantt,
                          boolean wantz,
                          int n,
                          int ilo,
                          int ihi,
                          double[] h,
                          int _h_offset,
                          int ldh,
                          double[] wr,
                          int _wr_offset,
                          double[] wi,
                          int _wi_offset,
                          int iloz,
                          int ihiz,
                          double[] z,
                          int _z_offset,
                          int ldz,
                          intW info)