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NAME
     dsyr2 - perform  the  symmetric  rank  2  operation    A  :=
     alpha*x*y' + alpha*y*x' + A

SYNOPSIS
     SUBROUTINE DSYR2 ( UPLO, N, ALPHA, X, INCX, Y, INCY, A,  LDA
               )

     DOUBLE PRECISION ALPHA

     INTEGER INCX, INCY, LDA, N

     CHARACTER*1 UPLO

     DOUBLE PRECISION A( LDA, * ), X( * ), Y( * )



     #include <sunperf.h>

     void dsyr2(char uplo, int n, double alpha, double  *dx,  int
               incx, double *dy, int incy, double *da, int lda) ;

PURPOSE
     DSYR2   performs  the  symmetric  rank  2  operation  A   :=
     alpha*x*y' + alpha*y*x' + A where alpha is a scalar, x and y
     are n element vectors and A is an n by n symmetric matrix.


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

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

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

               Unchanged on exit.

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

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

     X         - DOUBLE PRECISION array of dimension at least
               ( 1 + ( n - 1 )*abs( INCX ) ).  Before entry,  the
               incremented  array  X  must  contain the n element
               vector x.  Unchanged on exit.

     INCX      - INTEGER.
               On entry, INCX specifies  the  increment  for  the
               elements  of  X. INCX must not be zero.  Unchanged
               on exit.

     Y         - DOUBLE PRECISION array of dimension at least
               ( 1 + ( n - 1 )*abs( INCY ) ).  Before entry,  the
               incremented  array  Y  must  contain the n element
               vector y.  Unchanged on exit.

     INCY      - INTEGER.
               On entry, INCY specifies  the  increment  for  the
               elements  of  Y. INCY must not be zero.  Unchanged
               on exit.

     A         - DOUBLE PRECISION array of DIMENSION ( LDA, n ).
               Before entry with  UPLO = 'U' or 'u', the  leading
               n  by  n upper triangular part of the array A must
               contain the upper triangular part of the symmetric
               matrix and the strictly lower triangular part of A
               is not referenced. On exit, the  upper  triangular
               part  of  the  array A is overwritten by the upper
               triangular part of  the  updated  matrix.   Before
               entry  with  UPLO = 'L' or 'l', the leading n by n
               lower triangular part of the array A must  contain
               the  lower triangular part of the symmetric matrix
               and the strictly upper triangular part of A is not
               referenced.  On exit, the lower triangular part of
               the array A is overwritten by the lower triangular
               part of the updated matrix.

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

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