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## org.netlib.lapack
Class DTGEXC

    java.lang.Object
      org.netlib.lapack.DTGEXC

    public class DTGEXC

extends java.lang.Object

    DTGEXC is a simplified interface to the JLAPACK routine dtgexc.
    This interface converts Java-style 2D row-major arrays into
    the 1D column-major linearized arrays expected by the lower
    level JLAPACK routines.  Using this interface also allows you
    to omit offset and leading dimension arguments.  However, because
    of these conversions, these routines will be slower than the low
    level ones.  Following is the description from the original Fortran
    source.  Contact seymour@cs.utk.edu with any questions.

     *     ..
     *
     *  Purpose
     *  =======
     *
     *  DTGEXC reorders the generalized real Schur decomposition of a real
     *  matrix pair (A,B) using an orthogonal equivalence transformation
     *
     *                 (A, B) = Q * (A, B) * Z',
     *
     *  so that the diagonal block of (A, B) with row index IFST is moved
     *  to row ILST.
     *
     *  (A, B) must be in generalized real Schur canonical form (as returned

     *  by DGGES), i.e. A is block upper triangular with 1-by-1 and 2-by-2
     *  diagonal blocks. B is upper triangular.
     *
     *  Optionally, the matrices Q and Z of generalized Schur vectors are
     *  updated.
     *
     *         Q(in) * A(in) * Z(in)' = Q(out) * A(out) * Z(out)'
     *         Q(in) * B(in) * Z(in)' = Q(out) * B(out) * Z(out)'
     *
     *
     *  Arguments
     *  =========
     *
     *  WANTQ   (input) LOGICAL
     *          .TRUE. : update the left transformation matrix Q;
     *          .FALSE.: do not update Q.
     *
     *  WANTZ   (input) LOGICAL
     *          .TRUE. : update the right transformation matrix Z;
     *          .FALSE.: do not update Z.
     *
     *  N       (input) INTEGER
     *          The order of the matrices A and B. N >= 0.
     *
     *  A       (input/output) DOUBLE PRECISION array, dimension (LDA,N)
     *          On entry, the matrix A in generalized real Schur canonical
     *          form.
     *          On exit, the updated matrix A, again in generalized
     *          real Schur canonical form.
     *
     *  LDA     (input)  INTEGER
     *          The leading dimension of the array A. LDA >= max(1,N).
     *
     *  B       (input/output) DOUBLE PRECISION array, dimension (LDB,N)
     *          On entry, the matrix B in generalized real Schur canonical
     *          form (A,B).
     *          On exit, the updated matrix B, again in generalized
     *          real Schur canonical form (A,B).
     *
     *  LDB     (input)  INTEGER
     *          The leading dimension of the array B. LDB >= max(1,N).
     *
     *  Q       (input/output) DOUBLE PRECISION array, dimension (LDZ,N)
     *          On entry, if WANTQ = .TRUE., the orthogonal matrix Q.
     *          On exit, the updated matrix Q.
     *          If WANTQ = .FALSE., Q is not referenced.
     *
     *  LDQ     (input) INTEGER
     *          The leading dimension of the array Q. LDQ >= 1.
     *          If WANTQ = .TRUE., LDQ >= N.
     *
     *  Z       (input/output) DOUBLE PRECISION array, dimension (LDZ,N)
     *          On entry, if WANTZ = .TRUE., the orthogonal matrix Z.
     *          On exit, the updated matrix Z.
     *          If WANTZ = .FALSE., Z is not referenced.
     *
     *  LDZ     (input) INTEGER
     *          The leading dimension of the array Z. LDZ >= 1.
     *          If WANTZ = .TRUE., LDZ >= N.
     *
     *  IFST    (input/output) INTEGER
     *  ILST    (input/output) INTEGER
     *          Specify the reordering of the diagonal blocks of (A, B).
     *          The block with row index IFST is moved to row ILST, by a
     *          sequence of swapping between adjacent blocks.
     *          On exit, if IFST pointed on entry to the second row of
     *          a 2-by-2 block, it is changed to point to the first row;
     *          ILST always points to the first row of the block in its
     *          final position (which may differ from its input value by
     *          +1 or -1). 1 <= IFST, ILST <= N.
     *
     *  WORK    (workspace/output) DOUBLE PRECISION array, dimension (MAX(1,L
     *          On exit, if INFO = 0, WORK(1) returns the optimal LWORK.
     *
     *  LWORK   (input) INTEGER
     *          The dimension of the array WORK.
     *          LWORK >= 1 when N <= 1, otherwise LWORK >= 4*N + 16.
     *
     *          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.
     *
     *  INFO    (output) INTEGER
     *           =0:  successful exit.
     *           <0:  if INFO = -i, the i-th argument had an illegal value.
     *           =1:  The transformed matrix pair (A, B) would be too far
     *                from generalized Schur form; the problem is ill-
     *                conditioned. (A, B) may have been partially reordered,

     *                and ILST points to the first row of the current
     *                position of the block being moved.
     *
     *  Further Details
     *  ===============
     *
     *  Based on contributions by
     *     Bo Kagstrom and Peter Poromaa, Department of Computing Science,
     *     Umea University, S-901 87 Umea, Sweden.
     *
     *  [1] B. Kagstrom; A Direct Method for Reordering Eigenvalues in the
     *      Generalized Real Schur Form of a Regular Matrix Pair (A, B), in
     *      M.S. Moonen et al (eds), Linear Algebra for Large Scale and
     *      Real-Time Applications, Kluwer Academic Publ. 1993, pp 195-218.
     *
     *  =====================================================================
     *
     *     .. Parameters ..

Constructor Summary
`DTGEXC()`

Method Summary
`static void` | `DTGEXC(boolean wantq, boolean wantz, int n, double[][] a, double[][] b, double[][] q, double[][] z, intW ifst, intW ilst, double[] work, int lwork, intW info)`

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

Constructor Detail

### DTGEXC

    public DTGEXC()

Method Detail

### DTGEXC

    public static void DTGEXC(boolean wantq,
                              boolean wantz,
                              int n,
                              double[][] a,
                              double[][] b,
                              double[][] q,
                              double[][] z,
                              intW ifst,
                              intW ilst,
                              double[] work,
                              int lwork,
                              intW info)

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