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Technical Reference: Base Operating System and Extensions , Volume 2
Performs the symmetric rank 2
operation.
BLAS Library
(libblas.a)
SUBROUTINE SSYR2(UPLO, N, ALPHA, X,
INCX, Y, INCY, A, LDA)
REAL ALPHA
INTEGER INCX, INCY, LDA, N
CHARACTER*1 UPLO
REAL A(LDA,*), X(*), Y(*)
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(*)
The SSYR2 or
DSYR2 subroutine 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.
UPLO
 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
 On entry, N specifies the order of the matrix
A; N must be at least 0; unchanged on
exit.

ALPHA
 On entry, ALPHA specifies the scalar alpha; unchanged on
exit.

X
 A vector of dimension at least (1 + (N1) *
abs(INCX) ); on entry, the incremented array X must
contain the N element vector x; unchanged on exit.

INCX
 On entry, INCX specifies the increment for the elements of
X; INCX must not be 0; unchanged on
exit.

Y
 A vector of dimension at least (1 + (N1) *
abs(INCY) ); on entry, the incremented array Y must
contain the N element vector y; unchanged on exit.

INCY
 On entry, INCY specifies the increment for the elements of
Y; INCY must not be 0; unchanged on
exit.

A
 An array of dimension ( LDA, N ); on 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. On 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
 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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