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

Chapter 3 Basic Matrix Operations 281
Rank-2 update SSYR2/DSYR2/CHER2/ZHER2
incx < 0 x is stored backward in array x; that
is, x
i
is stored in x((i−n)×incx+1).
Use incx = 1 if the vector x is stored contiguously in
array x, that is, if x
i
is stored in x(i). Refer to “BLAS
Indexing Conventions” in the introduction to
Chapter 2.
y Array of length leny = (n−1)×|incy|+1 containing the
n-vector y.
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, 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.
a Array whose upper or lower triangle, as specified by
uplo, contains the upper or lower triangle of an n-by-n
real symmetric or complex Hermitian matrix A. The
other triangle of a is not referenced.
lda The leading dimension of array a as declared in the
calling program unit, with lda ≥ max(n,1).
Output a The upper or lower triangle of the updated A matrix, as
specified by uplo, replaces the upper or lower triangle
of the input, respectively. The other triangle of a is
unchanged.
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