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,

 

 

 

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.

 

 

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,

 

 

 

yi is stored in y((i−1)⋅incy+1).

 

 

incy < 0

y is stored backward in array y; that

 

 

 

is, yi is stored in y((i−n)⋅incy+1).

 

 

Use incy = 1 if the vector y is stored contiguously in

 

 

array y, that is, if yi 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-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 263