F06YRF (DSYR2K) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

NAG Library Routine Document

F06YRF (DSYR2K)

Note:  before using this routine, please read the Users' Note for your implementation to check the interpretation of bold italicised terms and other implementation-dependent details.

 Contents

    1  Purpose
    7  Accuracy
    10  Example

1  Purpose

F06YRF (DSYR2K) performs one of the symmetric rank-2k update operations
CαABT + αBAT + βC   or   CαATB + αBTA+βC ,  
where A and B are real matrices, C is an n by n real symmetric matrix, and α and β are real scalars.

2  Specification

SUBROUTINE F06YRF ( UPLO, TRANS, N, K, ALPHA, A, LDA, B, LDB, BETA, C, LDC)
INTEGER  N, K, LDA, LDB, LDC
REAL (KIND=nag_wp)  ALPHA, A(LDA,*), B(LDB,*), BETA, C(LDC,*)
CHARACTER(1)  UPLO, TRANS
The routine may be called by its BLAS name dsyr2k.

3  Description

None.

4  References

None.

5  Parameters

1:     UPLO – CHARACTER(1)Input
On entry: specifies whether the upper or lower triangular part of C is stored.
UPLO='U'
The upper triangular part of C is stored.
UPLO='L'
The lower triangular part of C is stored.
Constraint: UPLO='U' or 'L'.
2:     TRANS – CHARACTER(1)Input
On entry: specifies the operation to be performed.
TRANS='N'
CαABT+αBAT+βC.
TRANS='T' or 'C'
CαATB+αBTA+βC.
Constraint: TRANS='N', 'T' or 'C'.
3:     N – INTEGERInput
On entry: n, the order of the matrix C; the number of rows of A and B if TRANS='N', or the number of columns of A and B if TRANS='T' or 'C'.
Constraint: N0.
4:     K – INTEGERInput
On entry: k, the number of columns of A and B if TRANS='N', or the number of rows of A and B if TRANS='T' or 'C'.
Constraint: K0.
5:     ALPHA – REAL (KIND=nag_wp)Input
On entry: the scalar α.
6:     ALDA* – REAL (KIND=nag_wp) arrayInput
Note: the second dimension of the array A must be at least max1,K if TRANS='N' and at least max1,N if TRANS='T' or 'C'.
On entry: the matrix A; A is n by k if TRANS='N', or k by n if TRANS='T' or 'C'.
7:     LDA – INTEGERInput
On entry: the first dimension of the array A as declared in the (sub)program from which F06YRF (DSYR2K) is called.
Constraints:
  • if TRANS='N', LDA max1,N ;
  • if TRANS='T' or 'C', LDA max1,K .
8:     BLDB* – REAL (KIND=nag_wp) arrayInput
Note: the second dimension of the array B must be at least max1,K if TRANS='N' and at least max1,N if TRANS='T' or 'C'.
On entry: the matrix B; B is n by k if TRANS='N', or k by n if TRANS='T' or 'C'.
9:     LDB – INTEGERInput
On entry: the first dimension of the array B as declared in the (sub)program from which F06YRF (DSYR2K) is called.
Constraints:
  • if TRANS='N', LDB max1,N ;
  • if TRANS='T' or 'C', LDB max1,K .
10:   BETA – REAL (KIND=nag_wp)Input
On entry: the scalar β.
11:   CLDC* – REAL (KIND=nag_wp) arrayInput/Output
Note: the second dimension of the array C must be at least max1,N.
On entry: the n by n symmetric matrix C.
  • If UPLO='U', the upper triangular part of C must be stored and the elements of the array below the diagonal are not referenced.
  • If UPLO='L', the lower triangular part of C must be stored and the elements of the array above the diagonal are not referenced.
On exit: the updated matrix C.
12:   LDC – INTEGERInput
On entry: the first dimension of the array C as declared in the (sub)program from which F06YRF (DSYR2K) is called.
Constraint: LDCmax1,N .

6  Error Indicators and Warnings

None.

7  Accuracy

Not applicable.

8  Parallelism and Performance

Not applicable.

9  Further Comments

None.

10  Example

None.

F06YRF (DSYR2K) (PDF version)
F06 Chapter Contents
F06 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2015