NAG Library Function Document

nag_dsfrk (f16yqc)

 Contents

    1  Purpose
    7  Accuracy

1
Purpose

nag_dsfrk (f16yqc) performs one of the symmetric rank-k update operations
CαAAT + βC   or   CαATA + βC ,  
where A is a real matrix, C is an n by n real symmetric matrix stored in Rectangular Full Packed (RFP) format, and α and β are real scalars.

2
Specification

#include <nag.h>
#include <nagf16.h>
void  nag_dsfrk (Nag_OrderType order, Nag_RFP_Store transr, Nag_UploType uplo, Nag_TransType trans, Integer n, Integer k, double alpha, const double a[], Integer pda, double beta, double cr[], NagError *fail)

3
Description

nag_dsfrk (f16yqc) performs one of the symmetric rank-k update operations
CαAAT + βC   or   CαATA + βC ,  
where A is a real matrix, C is an n by n real symmetric matrix stored in Rectangular Full Packed (RFP) format, and α and β are real scalars. The RFP storage format is described in Section 3.3.3 in the f07 Chapter Introduction.
If n=0 or if β=1.0 and either k=0 or α=0.0 then nag_dsfrk (f16yqc) returns immediately. If β=0.0 and either k=0 or α=0.0 then C is set to the zero matrix.

4
References

Gustavson F G, Waśniewski J, Dongarra J J and Langou J (2010) Rectangular full packed format for Cholesky's algorithm: factorization, solution, and inversion ACM Trans. Math. Software 37, 2

5
Arguments

1:     order Nag_OrderTypeInput
On entry: the order argument specifies the two-dimensional storage scheme being used, i.e., row-major ordering or column-major ordering. C language defined storage is specified by order=Nag_RowMajor. See Section 3.3.1.3 in How to Use the NAG Library and its Documentation for a more detailed explanation of the use of this argument.
Constraint: order=Nag_RowMajor or Nag_ColMajor.
2:     transr Nag_RFP_StoreInput
On entry: specifies whether the RFP representation of C is normal or transposed.
transr=Nag_RFP_Normal
The matrix C is stored in normal RFP format.
transr=Nag_RFP_Trans
The matrix C is stored in transposed RFP format.
Constraint: transr=Nag_RFP_Normal or Nag_RFP_Trans.
3:     uplo Nag_UploTypeInput
On entry: specifies whether the upper or lower triangular part of C is stored in RFP format.
uplo=Nag_Upper
The upper triangular part of C is stored in RFP format.
uplo=Nag_Lower
The lower triangular part of C is stored in RFP format.
Constraint: uplo=Nag_Upper or Nag_Lower.
4:     trans Nag_TransTypeInput
On entry: specifies the operation to be performed.
trans=Nag_NoTrans
CαAAT+βC.
trans=Nag_Trans
CαATA+βC.
Constraint: trans=Nag_NoTrans or Nag_Trans.
5:     n IntegerInput
On entry: n, the order of the matrix C.
Constraint: n0.
6:     k IntegerInput
On entry: k, the number of columns of A if trans=Nag_NoTrans, or the number of rows of A if trans=Nag_Trans.
Constraint: k0.
7:     alpha doubleInput
On entry: the scalar α.
8:     a[dim] const doubleInput
Note: the dimension, dim, of the array a must be at least
  • max1,pda×k when trans=Nag_NoTrans and order=Nag_ColMajor;
  • max1,n×pda when trans=Nag_NoTrans and order=Nag_RowMajor;
  • max1,pda×n when trans=Nag_Trans and order=Nag_ColMajor;
  • max1,k×pda when trans=Nag_Trans and order=Nag_RowMajor.
On entry: the matrix A; A is n by k if trans=Nag_NoTrans, or k by n if trans=Nag_Trans. If alpha=0.0, a is not referenced.
9:     pda IntegerInput
On entry: the stride separating row or column elements (depending on the value of order) in the array a.
Constraints:
  • if order=Nag_ColMajor,
    • if trans=Nag_NoTrans, pda max1,n ;
    • if trans=Nag_Trans, pda max1,k ;
  • if order=Nag_RowMajor,
    • if trans=Nag_NoTrans, pdamax1,k;
    • if trans=Nag_Trans, pdamax1,n.
10:   beta doubleInput
On entry: the scalar β.
11:   cr[n×n+1/2] doubleInput/Output
On entry: the upper or lower triangular part (as specified by uplo) of the n by n symmetric matrix C, stored in RFP format (as specified by transr). The storage format is described in detail in Section 3.3.3 in the f07 Chapter Introduction. If β=0.0, cr need not be set on entry.
On exit: the updated matrix C, that is its upper or lower triangular part stored in RFP format.
12:   fail NagError *Input/Output
The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6
Error Indicators and Warnings

NE_ALLOC_FAIL
Dynamic memory allocation failed.
See Section 2.3.1.2 in How to Use the NAG Library and its Documentation for further information.
NE_BAD_PARAM
On entry, argument value had an illegal value.
NE_ENUM_INT_2
On entry, trans=value, k=value, pda=value.
Constraint: if trans=Nag_NoTrans, pdamax1,k.
On entry, trans=value, k=value, pda=value.
Constraint: if trans=Nag_Trans, pda max1,k .
On entry, trans=value, n=value, pda=value.
Constraint: if trans=Nag_NoTrans, pda max1,n .
On entry, trans=value, n=value, pda=value.
Constraint: if trans=Nag_Trans, pdamax1,n.
NE_INT
On entry, k=value.
Constraint: k0.
On entry, n=value.
Constraint: n0.
NE_INTERNAL_ERROR
An internal error has occurred in this function. Check the function call and any array sizes. If the call is correct then please contact NAG for assistance.
See Section 2.7.6 in How to Use the NAG Library and its Documentation for further information.
NE_NO_LICENCE
Your licence key may have expired or may not have been installed correctly.
See Section 2.7.5 in How to Use the NAG Library and its Documentation for further information.

7
Accuracy

Not applicable.

8
Parallelism and Performance

nag_dsfrk (f16yqc) makes calls to BLAS and/or LAPACK routines, which may be threaded within the vendor library used by this implementation. Consult the documentation for the vendor library for further information.
Please consult the x06 Chapter Introduction for information on how to control and interrogate the OpenMP environment used within this function. Please also consult the Users' Note for your implementation for any additional implementation-specific information.

9
Further Comments

None.

10
Example

This example reads in the lower triangular part of a symmetric matrix C which it converts to RFP format. It also reads in α, β and a 6 by 4 matrix A and then performs the symmetric rank-4 update CαAAT+βC.

10.1
Program Text

Program Text (f16yqce.c)

10.2
Program Data

Program Data (f16yqce.d)

10.3
Program Results

Program Results (f16yqce.r)

© The Numerical Algorithms Group Ltd, Oxford, UK. 2017