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NAME
     chbev - compute all the eigenvalues and, optionally,  eigen-
     vectors of a complex Hermitian band matrix A

SYNOPSIS
     SUBROUTINE CHBEV( JOBZ, UPLO, N, KD, AB, LDAB,  W,  Z,  LDZ,
               WORK, RWORK, INFO )

     CHARACTER JOBZ, UPLO

     INTEGER INFO, KD, LDAB, LDZ, N

     REAL RWORK( * ), W( * )

     COMPLEX AB( LDAB, * ), WORK( * ), Z( LDZ, * )



     #include <sunperf.h>

     void chbev(char jobz, char uplo,  int  n,  int  kd,  complex
               *cab,  int  ldab,  float *w, complex *cz, int ldz,
               int *info) ;

PURPOSE
     CHBEV computes all the eigenvalues and,  optionally,  eigen-
     vectors of a complex Hermitian band matrix A.


ARGUMENTS
     JOBZ      (input) CHARACTER*1
               = 'N':  Compute eigenvalues only;
               = 'V':  Compute eigenvalues and eigenvectors.

     UPLO      (input) CHARACTER*1
               = 'U':  Upper triangle of A is stored;
               = 'L':  Lower triangle of A is stored.

     N         (input) INTEGER
               The order of the matrix A.  N >= 0.

     KD        (input) INTEGER
               The number of superdiagonals of the  matrix  A  if
               UPLO  = 'U', or the number of subdiagonals if UPLO
               = 'L'.  KD >= 0.

     AB        (input/output) COMPLEX array, dimension (LDAB, N)
               On entry, the upper or lower triangle of the  Her-
               mitian  band  matrix  A,  stored in the first KD+1
               rows of the array.  The j-th column of A is stored
               in the j-th column of the array AB as follows:  if
               UPLO = 'U', AB(kd+1+i-j,j) = A(i,j)  for  max(1,j-
               kd)<=i<=j;  if UPLO = 'L', AB(1+i-j,j)    = A(i,j)
               for j<=i<=min(n,j+kd).

               On exit, AB is  overwritten  by  values  generated
               during the reduction to tridiagonal form.  If UPLO
               = 'U', the first superdiagonal and the diagonal of
               the  tridiagonal  matrix T are returned in rows KD
               and KD+1 of AB, and if UPLO =  'L',  the  diagonal
               and  first  subdiagonal  of  T are returned in the
               first two rows of AB.

     LDAB      (input) INTEGER
               The leading dimension of the array AB.  LDAB >= KD
               + 1.

     W         (output) REAL array, dimension (N)
               If INFO = 0, the eigenvalues in ascending order.

     Z         (output) COMPLEX array, dimension (LDZ, N)
               If JOBZ = 'V', then if INFO = 0,  Z  contains  the
               orthonormal eigenvectors of the matrix A, with the
               i-th column of Z holding the  eigenvector  associ-
               ated  with  W(i).   If  JOBZ  = 'N', then Z is not
               referenced.

     LDZ       (input) INTEGER
               The leading dimension of the array Z.  LDZ  >=  1,
               and if JOBZ = 'V', LDZ >= max(1,N).

     WORK      (workspace) COMPLEX array, dimension (N)

     RWORK     (workspace) REAL array, dimension (max(1,3*N-2))

     INFO      (output) INTEGER
               = 0:  successful exit.
               < 0:  if INFO = -i, the i-th argument had an ille-
               gal value.
               > 0:  if INFO = i, the algorithm  failed  to  con-
               verge;  i off-diagonal elements of an intermediate
               tridiagonal form did not converge to zero.

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