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

Chapter 3 Basic Matrix Operations 217
Matrix-vector multiply SGBMV/DGBMV/CGBMV/ZGBMV
Output y The updated y vector replaces the input.
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:
trans ≠ ’N’ or ’n’ or ’T’ or ’t’ or ’C’ or ’c’
m < 0
n < 0
kl < 0
ku < 0
ldab < kl+ku+1
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 trans argument as ’NORMAL’ or
’NONTRANS’ for ’N’, ’TRANSPOSE’ for ’T’, or ’CTRANS’ for ’C’. Refer to
“Example 2.”
Example 1 Form the REAL*4 matrix-vector product y = Ax, where A is a 9 by 6 real band
matrix whose lower bandwidth is 2 and whose upper bandwidth is 3. A is stored
in an array AB whose dimensions are 10 by 10, x is a real vector 6 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 TRANS
INTEGER*4 M,N,KL,KU,LDAB,INCX,INCY
REAL*4 ALPHA,BETA,AB(10,10),X(10),Y(10)
TRANS = ’N’
M = 9
N = 6
KL = 2
KU = 3
ALPHA = 1.0
BETA = 0.0
LDAB = 10
INCX = 1
INCY = 1
CALL SGBMV (TRANS,M,N,KL,KU,ALPHA,AB,LDAB,X,INCX,BETA,Y,INCY)