DSYR2  performs the symmetric rank 2 operation


    A := alpha*x*y**T + alpha*y*x**T + A,


 where alpha is a scalar, x and y are n element vectors and A is an n


 by n symmetric matrix.

UPLO

          UPLO is 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.

N

          N is INTEGER


           On entry, N specifies the order of the matrix A.


           N must be at least zero.

ALPHA

          ALPHA is DOUBLE PRECISION.


           On entry, ALPHA specifies the scalar alpha.

X

          X is 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.

INCX

          INCX is INTEGER


           On entry, INCX specifies the increment for the elements of


           X. INCX must not be zero.

Y

          Y is 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.

INCY

          INCY is INTEGER


           On entry, INCY specifies the increment for the elements of


           Y. INCY must not be zero.

A

          A is 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

          LDA is 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 ).

Univ. of Tennessee

Univ. of California Berkeley

Univ. of Colorado Denver

NAG Ltd.

November 2011

  Level 2 Blas routine.


  -- Written on 22-October-1986.


     Jack Dongarra, Argonne National Lab.


     Jeremy Du Croz, Nag Central Office.


     Sven Hammarling, Nag Central Office.


     Richard Hanson, Sandia National Labs.