HP MLIB User's Guide Vol. 1 7th Ed.

264 HP MLIB User’s Guide
SSPR2/DSPR2/CHPR2/ZHPR2 Rank-2 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
incx = 0
incy = 0
Actual character arguments in a subroutine call may be longer than the
corresponding dummy arguments. Therefore, readability of the CALL
statement can 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-2 update xy
T
+x
T
y to A, where A is a 9-by-9
real symmetric matrix whose upper triangle is stored in packed form in an
array AP of dimension 55, x is a real vector 9 elements long stored in an array X
of dimension 10, and y is a real vector 9 elements long stored in an array Y also
of dimension 10.
CHARACTER*1 UPLO
INTEGER*4 N,INCX,INCY
REAL*4 ALPHA,AP(55),X(10),Y(10)
UPLO = ’U’
N = 9
ALPHA = 1.0
INCX = 1
INCY = 1
CALL SSPR2 (UPLO,N,ALPHA,X,INCX,Y,INCY,AP)
Example 2 Apply a COMPLEX*8 Hermitian rank-2 update to A, where A is a
9-by-9 complex Hermitian matrix whose lower triangle is stored in packed form
in an array AP of dimension 55, α is a complex scalar, x is a complex vector 9
elements long stored in an array X of dimension 10, and y is a complex vector 9
elements long stored in an array Y of dimension 10.
INTEGER*4 N
COMPLEX*8 ALPHA,AP(55),X(10),Y(10)
N = 9
CALL CHPR2 (’LOWER’,N,ALPHA,X,1,Y,1,AP)
αxy*+αyx*