ZSYR2K

# ZSYR2K

Section: BLAS routine (3) Updated: 16 October 1992
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## NAME

ZSYR2K - perform one of the symmetric rank 2k operations C := alpha*A*B' + alpha*B*A' + beta*C,

## SYNOPSIS

SUBROUTINE ZSYR2K(
UPLO, TRANS, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC )

CHARACTER*1 UPLO, TRANS

INTEGER N, K, LDA, LDB, LDC

COMPLEX*16 ALPHA, BETA

COMPLEX*16 A( LDA, * ), B( LDB, * ), C( LDC, * )

## PURPOSE

ZSYR2K performs one of the symmetric rank 2k operations

or

C := alpha*A'*B + alpha*B'*A + beta*C,

where alpha and beta are scalars, C is an n by n symmetric matrix and A and B are n by k matrices in the first case and k by n matrices in the second case.

## PARAMETERS

UPLO - CHARACTER*1.
On entry, UPLO specifies whether the upper or lower triangular part of the array C is to be referenced as follows:

UPLO = 'U' or 'u' Only the upper triangular part of C is to be referenced.

UPLO = 'L' or 'l' Only the lower triangular part of C is to be referenced.

Unchanged on exit.

TRANS - CHARACTER*1.
On entry, TRANS specifies the operation to be performed as follows:

TRANS = 'N' or 'n' C := alpha*A*B' + alpha*B*A' + beta*C.

TRANS = 'T' or 't' C := alpha*A'*B + alpha*B'*A + beta*C.

Unchanged on exit.

N - INTEGER.
On entry, N specifies the order of the matrix C. N must be at least zero. Unchanged on exit.
K - INTEGER.
On entry with TRANS = 'N' or 'n', K specifies the number of columns of the matrices A and B, and on entry with TRANS = 'T' or 't', K specifies the number of rows of the matrices A and B. K must be at least zero. Unchanged on exit.
ALPHA - COMPLEX*16 .
On entry, ALPHA specifies the scalar alpha. Unchanged on exit.
A - COMPLEX*16 array of DIMENSION ( LDA, ka ), where ka is
k when TRANS = 'N' or 'n', and is n otherwise. Before entry with TRANS = 'N' or 'n', the leading n by k part of the array A must contain the matrix A, otherwise the leading k by n part of the array A must contain the matrix A. Unchanged on exit.
LDA - INTEGER.
On entry, LDA specifies the first dimension of A as declared in the calling (sub) program. When TRANS = 'N' or 'n' then LDA must be at least max( 1, n ), otherwise LDA must be at least max( 1, k ). Unchanged on exit.
B - COMPLEX*16 array of DIMENSION ( LDB, kb ), where kb is
k when TRANS = 'N' or 'n', and is n otherwise. Before entry with TRANS = 'N' or 'n', the leading n by k part of the array B must contain the matrix B, otherwise the leading k by n part of the array B must contain the matrix B. Unchanged on exit.
LDB - INTEGER.
On entry, LDB specifies the first dimension of B as declared in the calling (sub) program. When TRANS = 'N' or 'n' then LDB must be at least max( 1, n ), otherwise LDB must be at least max( 1, k ). Unchanged on exit.
BETA - COMPLEX*16 .
On entry, BETA specifies the scalar beta. Unchanged on exit.
C - COMPLEX*16 array of DIMENSION ( LDC, n ).
Before entry with UPLO = 'U' or 'u', the leading n by n upper triangular part of the array C must contain the upper triangular part of the symmetric matrix and the strictly lower triangular part of C is not referenced. On exit, the upper triangular part of the array C 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 C must contain the lower triangular part of the symmetric matrix and the strictly upper triangular part of C is not referenced. On exit, the lower triangular part of the array C is overwritten by the lower triangular part of the updated matrix.
LDC - INTEGER.
On entry, LDC specifies the first dimension of C as declared in the calling (sub) program. LDC must be at least max( 1, n ). Unchanged on exit.

Level 3 Blas routine.

-- Written on 8-February-1989. Jack Dongarra, Argonne National Laboratory. Iain Duff, AERE Harwell. Jeremy Du Croz, Numerical Algorithms Group Ltd. Sven Hammarling, Numerical Algorithms Group Ltd.

## Index

NAME
SYNOPSIS
PURPOSE
PARAMETERS

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