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

## SSYR2K, DSYR2K, CSYR2K, or ZSYR2K Subroutine

### Purpose

Performs symmetric rank 2k operations.

### Library

BLAS Library (**libblas.a**)

### FORTRAN Syntax

**SUBROUTINE** **SSYR2K(***UPLO***, ***TRANS***, ***N***, ***K***, ***ALPHA***,**
*A***, ***LDA***, ***B***, ***LDB***, ***BETA***, ***C***, ***LDC***)**
**CHARACTER*1** *UPLO***,***TRANS*
**INTEGER** *N***,***K***,***LDA***,***LDB***,***LDC*
**REAL** *ALPHA***,***BETA*
**REAL** *A***(***LDA***,*), ***B***(***LDB***,*), ***C***(***LDC***,*)**

**SUBROUTINE** **DSYR2K(***UPLO***, ***TRANS***, ***N***, ***K***, ***ALPHA***,**
*A***, ***LDA***, ***B***, ***LDB***, ***BETA***, ***C***, ***LDC***)**
**CHARACTER*1** *UPLO***,***TRANS*
**INTEGER** *N***,***K***,***LDA***,***LDB***,***LDC*
**DOUBLE PRECISION** *ALPHA***,***BETA*
**DOUBLE PRECISION** *A***(***LDA***,*), ***B***(***LDB***,*), ***C***(***LDC***,*)**

**SUBROUTINE** **CSYR2K(***UPLO***, ***TRANS***, ***N***, ***K***, ***ALPHA***,**
*A***, ***LDA***, ***B***, ***LDB***, ***BETA***, ***C***, ***LDC***)**
**CHARACTER*1** *UPLO***,***TRANS*
**INTEGER** *N***,***K***,***LDA***,***LDB***,***LDC*
**COMPLEX** *ALPHA***,***BETA*
**COMPLEX** *A***(***LDA***,*), ***B***(***LDB***,*), ***C***(***LDC***,*)**

**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***,*)**

### Description

The **SSYR2K**, **DSYR2K**, **CSYR2K**, or **ZSYR2K** subroutine performs one of the symmetric rank 2k operations:

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

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* |
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* |
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* |
On entry, *N* specifies the order of the matrix *C;* *N* must be at least 0; unchanged on exit. |

*K* |
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 0; unchanged on exit. |

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

*A* |
An array of dimension ( *LDA*, *KA* ), where *KA* is *K* when *TRANS* = 'N' or 'n', and is *N* otherwise; on 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* |
On entry, *LDA* specifies the first dimension of *A* as declared in the calling (sub) program. When *TRANS* = 'N' or 'n', *LDA* must be at least max( 1, *N* ); otherwise *LDA* must be at least max( 1, *K* ); unchanged on exit. |

*B* |
An array of dimension ( *LDB*, *KB* ), where *KB* is *K* when *TRANS* = 'N' or 'n', and is *N* otherwise; on 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* |
On entry, *LDB* specifies the first dimension of *B* as declared in the calling (sub) program. When *TRANS *= 'N' or 'n', *LDB* must be at least max( 1, *N* ); otherwise *LDB* must be at least max( 1, *K* ); unchanged on exit. |

*BETA* |
On entry, *BETA* specifies the scalar beta; unchanged on exit. |

*C* |
An array of dimension ( *LDC*, *N* ); on 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. On 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* |
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. |

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