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

Chapter 3 Basic Matrix Operations 257

Rank-1 update SSPR/DSPR/CHPR/ZHPR

Input uplo Upper/lower triangular option for A:

’L’ or ’l’ The lower triangle of A is stored in the

packed array.

’U’ or ’u’ The upper triangle of A is stored in

the packed array.

n Number of rows and columns in matrix A and elements

of vector x, n ≥ 0. If n = 0, the subprograms do not

reference ap or x.

alpha The scalar α. If alpha = 0, the subprograms do not

reference ap or x.

x Array of length lenx = (n−1)×|incx|+1 containing the

n-vector x.

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.

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.