SSYR/DSYR/CHER/ZHER

Rank-1 update

Notes These subprograms conform to specifications of the Level 2 BLAS.

If an error in the arguments is detected, the subprograms call error handler XERBLA, which writes an error message onto the standard error file and terminates execution. The standard version of XERBLA (refer to the end of this chapter) can be replaced with a user-supplied version to change the error procedure. Error conditions are

uplo ≠ ’L’ or ’l’ or ’U’ or ’u’ n < 0

lda < max(n,1) incx = 0

Actual character arguments in a subroutine call can be longer than the corresponding dummy arguments. Therefore, readability of the CALL statement may be improved by coding the uplo argument as ’LOWER’ for ’L’ or ’UPPER’ for ’U’. Refer to “Example 2.”

Example 1 Apply a REAL*4 symmetric rank-1 update xxT to A, where A is a 9-by-9 real symmetric matrix whose upper triangle is stored in the upper triangle of an array A whose dimensions are 10-by-10, and x is a real vector 9 elements long stored in an array X of dimension 10.

CHARACTER*1 UPLO

INTEGER*4 N,LDA,INCX

REAL*4 ALPHA,A(10,10),X(10)

UPLO = ’U’

N = 9

ALPHA = 1.0

LDA = 10

INCX = 1

CALL SSYR (UPLO,N,ALPHA,X,INCX,A,LDA)

Example 2 Apply a COMPLEX*8 Hermitian rank-1 update −2xx* to A, where A is a 9-by-9 complex Hermitian matrix whose lower triangle is stored in the lower triangle of an array A whose dimensions are 10-by-10, and x is a complex vector 9 elements long stored in an array X of dimension 10.

INTEGER*4

N,LDA

COMPLEX*8

A(10,10),X(10)

N =

9

 

LDA

= 10

 

CALL CHER

(’LOWER’,N,-2.0,X,1,A,LDA)

278HP MLIB User’s Guide