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NAME
     zhegst - reduce  a  complex  Hermitian-definite  generalized
     eigenproblem to standard form

SYNOPSIS
     SUBROUTINE ZHEGST( ITYPE, UPLO, N, A, LDA, B, LDB, INFO )

     CHARACTER UPLO

     INTEGER INFO, ITYPE, LDA, LDB, N

     COMPLEX*16 A( LDA, * ), B( LDB, * )



     #include <sunperf.h>

     void zhegst(int itype, char uplo, int n, doublecomplex  *za,
               int lda, doublecomplex *zb, int ldb, int *info) ;

PURPOSE
     ZHEGST  reduces  a  complex  Hermitian-definite  generalized
     eigenproblem to standard form.

     If ITYPE = 1, the problem is A*x = lambda*B*x,
     and   A   is   overwritten    by    inv(U**H)*A*inv(U)    or
     inv(L)*A*inv(L**H)

     If ITYPE = 2 or 3, the problem is A*B*x = lambda*x or
     B*A*x = lambda*x,  and  A  is  overwritten  by  U*A*U**H  or
     L**H*A*L.

     B must have been previously factorized as U**H*U  or  L*L**H
     by ZPOTRF.


ARGUMENTS
     ITYPE     (input) INTEGER
               =     1:     compute     inv(U**H)*A*inv(U)     or
               inv(L)*A*inv(L**H);
               = 2 or 3: compute U*A*U**H or L**H*A*L.

     UPLO      (input) CHARACTER
               = 'U':  Upper triangle of A is  stored  and  B  is
               factored as U**H*U; = 'L':  Lower triangle of A is
               stored and B is factored as L*L**H.

     N         (input) INTEGER
               The order of the matrices A and B.  N >= 0.

     A         (input/output) COMPLEX*16 array, dimension (LDA,N)
               On entry, the Hermitian matrix A.  If UPLO =  'U',
               the leading N-by-N upper triangular part of A con-
               tains the upper triangular part of the  matrix  A,
               and the strictly lower triangular part of A is not
               referenced.  If UPLO =  'L',  the  leading  N-by-N
               lower triangular part of A contains the lower tri-
               angular part of the matrix  A,  and  the  strictly
               upper triangular part of A is not referenced.

               On exit, if INFO  =  0,  the  transformed  matrix,
               stored in the same format as A.

     LDA       (input) INTEGER
               The leading dimension of  the  array  A.   LDA  >=
               max(1,N).

     B         (input) COMPLEX*16 array, dimension (LDB,N)
               The triangular factor from the Cholesky factoriza-
               tion of B, as returned by ZPOTRF.

     LDB       (input) INTEGER
               The leading dimension of  the  array  B.   LDB  >=
               max(1,N).

     INFO      (output) INTEGER
               = 0:  successful exit
               < 0:  if INFO = -i, the i-th argument had an ille-
               gal value

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