SSYR2K(3)       BLAS routine of NEC Numeric Library Collection       SSYR2K(3)



NAME
       SSYR2K  -  perform  one  of  the  symmetric  rank  2k operations   C :=
       alpha*A*B' + alpha*B*A' + beta*C,   C  :=  alpha*A'*B  +  alpha*B'*A  +
       beta*C

SYNOPSIS
       SUBROUTINE SSYR2K( UPLO,  TRANS,  N, K, ALPHA, A, LDA, B, LDB, BETA, C,
                          LDC )

           CHARACTER*1    UPLO, TRANS

           INTEGER        N, K, LDA, LDB, LDC

           REAL           ALPHA, BETA

           REAL           A( LDA, * ), B( LDB, * ), C( LDC, * )

PURPOSE
       SSYR2K  performs one of the symmetric rank 2k operations
          C := alpha*A*B' + alpha*B*A' + beta*C
       or
          C := alpha*A'*B + alpha*B'*A + beta*C

       where  alpha and beta  are scalars, C is an  n by n   symmetric  matrix
       and   A  and B  are  n by k  matrices  in the  first  case  and  k by n
       matrices 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*B' + alpha*B*A' + beta*C.

              TRANS = 'T' or 't'   C := alpha*A'*B + alpha*B'*A + beta*C.

              TRANS = 'C' or 'c'   C := alpha*A'*B + alpha*B'*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  matrices  A and B,  and on  entry  with TRANS =
              'T' or 't' or 'C' or 'c',  K  specifies  the  number of rows  of
              the  matrices  A and B.  K must be at least  zero.  Unchanged on
              exit.

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

       A      - REAL             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.

       B      - REAL             array of DIMENSION ( LDB, kb ), where kb 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  B  must contain the matrix  B,  otherwise the leading
              k  by  n   part  of  the  array   B  must contain  the matrix B.
              Unchanged on exit.

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

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

       C      - REAL             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  symmetric 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   symmet-
              ric  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.

       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                      SSYR2K(3)