debian man page for dsyr2

DSYR2(3)							   BLAS routine 							  DSYR2(3)

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( * )

PURPOSE
       DSYR2  performs the symmetric rank 2 operation

       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  triangu-
	      lar  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.

	      Level 2 Blas routine.

	      -- Written on 22-October-1986.  Jack Dongarra, Argonne National Lab.  Jeremy Du Croz, Nag Central Office.  Sven Hammarling, Nag Cen-
	      tral Office.  Richard Hanson, Sandia National Labs.

BLAS routine							  16 October 1992							  DSYR2(3)