ZHERK(3)        BLAS routine of NEC Numeric Library Collection        ZHERK(3)



NAME
       ZHERK  -  perform  one  of  the  hermitian  rank  k  operations   C  :=
       alpha*A*conjg( A' ) + beta*C,  C := alpha*conjg( A' )*A + beta*C

SYNOPSIS
       SUBROUTINE ZHERK ( UPLO, TRANS, N, K, ALPHA, A, LDA, BETA, C, LDC )

           CHARACTER*1  UPLO, TRANS

           INTEGER      N, K, LDA, LDC

           DOUBLE       PRECISION ALPHA, BETA

           COMPLEX*16   A( LDA, * ), C( LDC, * )

PURPOSE
       ZHERK  performs one of the hermitian rank k operations
          C := alpha*A*conjg( A' ) + beta*C or
          C := alpha*conjg( A' )*A + beta*C,

       where  alpha and beta  are  real scalars,  C is an  n by  n   hermitian
       matrix  and   A  is an  n by k  matrix in the  first case and a  k by n
       matrix in the second case.


PARAMETERS
       UPLO   - CHARACTER*1.
              On  entry,   UPLO  specifies  whether   the   upper   or   lower
              triangular   part   of  the   array  C  is to be  referenced  as
              follows:

              UPLO = 'U' or 'u'   Only the  upper triangular part of  C is  to
              be referenced.

              UPLO  = 'L' or 'l'   Only the  lower triangular part of  C is to
              be referenced.

              Unchanged on exit.

       TRANS  - CHARACTER*1.
              On entry,  TRANS  specifies the operation  to  be  performed  as
              follows:

              TRANS = 'N' or 'n'   C := alpha*A*conjg( A' ) + beta*C.

              TRANS = 'C' or 'c'   C := alpha*conjg( A' )*A + beta*C.

              Unchanged on exit.

       N      - INTEGER.
              On  entry,  N specifies the order of the matrix C.  N must be at
              least zero.  Unchanged on exit.

       K      - INTEGER.
              On entry with  TRANS = 'N' or 'n',  K  specifies  the number  of
              columns   of  the   matrix   A,   and  on   entry   with TRANS =
              'C' or 'c',  K  specifies  the number of rows of the  matrix  A.
              K must be at least zero.  Unchanged on exit.

       ALPHA  - DOUBLE PRECISION.
              On  entry, ALPHA specifies the scalar alpha.  Unchanged on exit.

       A      - COMPLEX*16       array of DIMENSION ( LDA, ka ), where ka is
              k  when  TRANS = 'N' or 'n',   and  is   n   otherwise.   Before
              entry  with   TRANS  = 'N' or 'n',  the  leading  n by k part of
              the array  A  must contain the matrix  A,  otherwise the leading
              k  by  n   part  of  the  array   A  must contain  the matrix A.
              Unchanged on exit.

       LDA    - INTEGER.
              On entry, LDA specifies the first dimension of A as declared  in
              the   calling   (sub)   program.   When  TRANS = 'N' or 'n' then
              LDA must be at least  max( 1, n ), otherwise   LDA  must  be  at
              least  max( 1, k ).  Unchanged on exit.

       BETA   - DOUBLE PRECISION.
              On entry, BETA specifies the scalar beta.  Unchanged on exit.

       C      - COMPLEX*16       array of DIMENSION ( LDC, n ).
              Before  entry   with   UPLO  =  'U' or 'u',  the leading  n by n
              upper triangular part of the array C must contain the upper tri-
              angular  part   of the  hermitian matrix  and the strictly lower
              triangular part of C is not referenced.  On exit, the upper tri-
              angular  part of the array  C is overwritten by the upper trian-
              gular part of the updated matrix.  Before entry   with   UPLO  =
              'L'  or  'l',   the leading  n by n lower triangular part of the
              array C must contain the lower triangular part  of  the   hermi-
              tian  matrix  and the strictly upper triangular part of C is not
              referenced.  On exit, the lower triangular part of the array   C
              is  overwritten  by  the  lower  triangular  part of the updated
              matrix.  Note that the imaginary parts of the diagonal  elements
              need not be set,  they are assumed to be zero,  and on exit they
              are set to zero.

       LDC    - INTEGER.
              On entry, LDC specifies the first dimension of C as declared  in
              the  calling  (sub)  program.   LDC  must  be  at  least max( 1,
              n ).  Unchanged on exit.

              Level 3 Blas routine.

              -- Written on 8-February-1989.  Jack Dongarra, Argonne  National
              Laboratory.  Iain Duff, AERE Harwell.  Jeremy Du Croz, Numerical
              Algorithms Group Ltd.   Sven  Hammarling,  Numerical  Algorithms
              Group Ltd.



BLAS routine                    16 October 1992                       ZHERK(3)