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AIX Version 4.3 Base Operating System and Extensions Technical Reference, Volume 2

## SSYR2 or DSYR2 Subroutine

### Purpose

Performs the symmetric rank 2 operation.

### Library

BLAS Library (libblas.a)

### FORTRAN Syntax

```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(*)```

### Description

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.

### Parameters

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 + (N-1) * 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 + (N-1) * 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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