C Library Functions - dsyr2 (3)

NAME

dsyr2(3f) - [BLAS:DOUBLE_BLAS_LEVEL2]

Synopsis
Definition
Options
A
Authors
Further Details
See Also

SYNOPSIS

subroutine dsyr2(uplo,n,alpha,x,incx,y,incy,a,lda)

      .. Scalar Arguments ..
      double precision,intent(in)    :: alpha
      integer,intent(in)             :: incx,incy,lda,n
      character,intent(in)           :: uplo
      ..
      .. Array Arguments ..
      double precision,intent(inout) :: a(lda,*)
      double precision,intent(in)    :: x(*),y(*)
      ..

DEFINITION

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.

OPTIONS

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, 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, 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, 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 ).

AUTHORS

o Univ. of Tennessee

o Univ. of California Berkeley

o Univ. of Colorado Denver

o NAG Ltd.
 date:December 2016

FURTHER DETAILS

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.