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

Chapter 3 Basic Matrix Operations 263

Rank-2 update SSPR2/DSPR2/CHPR2/ZHPR2

incx Increment for the array x, incx ≠ 0:

incx > 0 x is stored forward in array x; that is,

is stored in x((i−1)×incx+1).

incx < 0 x is stored backward in array x; that

is, x

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

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,

is stored in y((i−1)×incy+1).

incy < 0 y is stored backward in array y; that

is, y

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

is stored in y(i). Refer to “BLAS

Indexing Conventions” in the introduction to

Chapter 2.

ap Array of length lenap = n×(n+1)/2 containing the upper

or lower triangle, as speciﬁed by uplo, of an n-by-n real

symmetric or complex Hermitian matrix A, stored by

columns in the packed form described above.

Output ap The upper or lower triangle of the updated A matrix, as

speciﬁed by uplo, replaces the input.