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

Chapter 3 Basic Matrix Operations 235
Matrix-vector multiply SGEMV/DGEMV/CGEMV/ZGEMV
y Array containing the vector y. The number of elements
of y and the value of leny, the dimension of the array y,
depend on trans:
Not used as input if beta = 0.
incy Increment for the array y, incy ≠ 0:
incy > 0 y is stored forward in array y; that is,
y
i
is stored in y((i−1)×incy+1).
incy < 0 y is stored backward in array y; that
is, if trans = ’N’ or ’n’, then y
i
is stored
in y((i−m)×incy+1); otherwise, y
i
is
stored in y((i−n)×incy+1).
Use incy = 1 if the vector y is stored contiguously in
array y, that is, if y
i
is stored in y(i). Refer to “BLAS
Indexing Conventions” in the introduction to
Chapter 2.
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
lda < max(m,1)
incx = 0
incy = 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 trans argument as ’NORMAL’ or
’NONTRANS’ for ’N’, ’TRANSPOSE’ for ’T’, or ’CTRANS’ for ’C’. Refer to
“Example 2.”
’N’ or ’n’ y has m elements leny = (m−1)×|incy|+1
otherwise y has n elements leny = (n−1)×|incy|+1