NAG FL Interface
f06ppf (dsyr)

1 Purpose

f06ppf computes the rank-1 update of a real symmetric matrix.

2 Specification

Fortran Interface
Subroutine f06ppf ( uplo, n, alpha, x, incx, a, lda)
Integer, Intent (In) :: n, incx, lda
Real (Kind=nag_wp), Intent (In) :: alpha, x(*)
Real (Kind=nag_wp), Intent (Inout) :: a(lda,*)
Character (1), Intent (In) :: uplo
C Header Interface
#include <nag.h>
void  f06ppf_ (const char *uplo, const Integer *n, const double *alpha, const double x[], const Integer *incx, double a[], const Integer *lda, const Charlen length_uplo)
The routine may be called by the names f06ppf, nagf_blas_dsyr or its BLAS name dsyr.

3 Description

f06ppf performs the symmetric rank-1 update operation
AαxxT+A ,  
where A is an n by n real symmetric matrix, x is an n-element real vector, and α is a real scalar.

4 References

None.

5 Arguments

1: uplo Character(1) Input
On entry: specifies whether the upper or lower triangular part of A is stored.
uplo='U'
The upper triangular part of A is stored.
uplo='L'
The lower triangular part of A is stored.
Constraint: uplo='U' or 'L'.
2: n Integer Input
On entry: n, the order of the matrix A.
Constraint: n0.
3: alpha Real (Kind=nag_wp) Input
On entry: the scalar α.
4: x* Real (Kind=nag_wp) array Input
Note: the dimension of the array x must be at least max1, 1+n-1 ×incx .
On entry: the n-element vector x.
If incx>0, xi must be stored in x1+i-1×incx, for i=1,2,,n.
If incx<0, xi must be stored in x1-n-i×incx, for i=1,2,,n.
Intermediate elements of x are not referenced.
5: incx Integer Input
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
6: alda* Real (Kind=nag_wp) array Input/Output
Note: the second dimension of the array a must be at least max1,n.
On entry: the n by n symmetric matrix A.
  • If uplo='U', the upper triangular part of A must be stored and the elements of the array below the diagonal are not referenced.
  • If uplo='L', the lower triangular part of A must be stored and the elements of the array above the diagonal are not referenced.
On exit: the updated matrix A.
7: lda Integer Input
On entry: the first dimension of the array a as declared in the (sub)program from which f06ppf is called.
Constraint: lda max1,n .

6 Error Indicators and Warnings

None.

7 Accuracy

Not applicable.

8 Parallelism and Performance

f06ppf is not threaded in any implementation.

9 Further Comments

None.

10 Example

None.