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,

 

 

 

xi is stored in x((i−1)⋅incx+1).

 

 

incx < 0

x is stored backward in array x; that

 

 

 

is, xi is stored in x((i−n)⋅incx+1).

 

 

Use incx = 1 if the vector x is stored contiguously in

 

 

array x, that is, if xi 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-nreal

 

 

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.

Chapter 3 Basic Matrix Operations 257