##### gges

###### Prototype

There are two prototypes of `gges` available, please see below.

    gges( const char jobvsl, const char jobvsr, const char sort,
            external_fp selctg, MatrixA& a, MatrixB& b, int_t& sdim,
            VectorALPHAR& alphar, VectorALPHAI& alphai, VectorBETA& beta,
            MatrixVSL& vsl, MatrixVSR& vsr );

    gges( const char jobvsl, const char jobvsr, const char sort,
            external_fp selctg, MatrixA& a, MatrixB& b, int_t& sdim,
            VectorALPHA& alpha, VectorBETA& beta, MatrixVSL& vsl, MatrixVSR& vsr );

###### Description

`gges` (short for $FRIENDLY_NAME) provides a C++ interface to LAPACK routines SGGES, DGGES, CGGES, and ZGGES. `gges` computes for a pair of N-by-N complex nonsymmetric matrices (A,B), the generalized eigenvalues, the generalized complex Schur form (S, T), and optionally left and/or right Schur vectors (VSL and VSR). This gives the generalized Schur factorization

(A,B) = ( (VSL)S(VSR)**H, (VSL)T(VSR)**H )

where (VSR)**H is the conjugate-transpose of VSR.

Optionally, it also orders the eigenvalues so that a selected cluster of eigenvalues appears in the leading diagonal blocks of the upper triangular matrix S and the upper triangular matrix T. The leading columns of VSL and VSR then form an unitary basis for the corresponding left and right eigenspaces (deflating subspaces).

(If only the generalized eigenvalues are needed, use the driver ZGGEV instead, which is faster.)

A generalized eigenvalue for a pair of matrices (A,B) is a scalar w or a ratio alpha/beta = w, such that A - w*B is singular. It is usually represented as the pair (alpha,beta), as there is a reasonable interpretation for beta=0, and even for both being zero.

A pair of matrices (S,T) is in generalized complex Schur form if S and T are upper triangular and, in addition, the diagonal elements of T are non-negative real numbers.

The selection of the LAPACK routine is done during compile-time, and is determined by the type of values contained in type `MatrixA`. The type of values is obtained through the `value_type` meta-function `typename value_type<MatrixA>::type`. The dispatching table below illustrates to which specific routine the code path will be generated.

Table 1.102. Dispatching of gges

Value type of MatrixA | LAPACK routine
--- | ---
`float` | SGGES
`double` | DGGES
`complex<float>` | CGGES
`complex<double>` | ZGGES

###### Definition

Defined in header `boost/numeric/bindings/lapack/driver/gges.hpp`.

###### Parameters or Requirements on Types

Parameters

MatrixA

  The definition of term 1

MatrixB

  The definition of term 2

MatrixC

  The definition of term 3.

  Definitions may contain paragraphs.

###### Complexity

###### Example

    #include <boost/numeric/bindings/lapack/driver/gges.hpp>
    using namespace boost::numeric::bindings;

    lapack::gges( x, y, z );

this will output

    [5] 0 1 2 3 4 5

###### Notes

###### See Also

- Originating Fortran source files sgges.f, dgges.f, cgges.f, and zgges.f at Netlib.