# csyrk

```CSYRK(1)                         BLAS routine                         CSYRK(1)

NAME
CSYRK - performs one of the symmetric rank k operations   C :=
alpha*A*A' + beta*C,

SYNOPSIS
SUBROUTINE CSYRK(UPLO,TRANS,N,K,ALPHA,A,LDA,BETA,C,LDC)

COMPLEX                                             ALPHA,BETA

INTEGER                                             K,LDA,LDC,N

CHARACTER                                           TRANS,UPLO

COMPLEX                                             A(LDA,*),C(LDC,*)

PURPOSE
CSYRK  performs one of the symmetric rank k operations

or

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

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

ARGUMENTS
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*A' + beta*C.

TRANS = 'T' or 't'   C := alpha*A'*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   matrix   A,   and  on   entry   with TRANS =
'T' or 't',  K  specifies  the number of rows of the matrix A.
K must be at least zero.  Unchanged on exit.

ALPHA  - COMPLEX         .
On entry, ALPHA specifies the scalar alpha.  Unchanged on exit.

A      - COMPLEX          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.

BETA   - COMPLEX         .
On entry, BETA specifies the scalar beta.  Unchanged on exit.

C      - COMPLEX          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.

FURTHER DETAILS
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.

BLAS routine                     November 2008                        CSYRK(1)```