nag_dger (f16pmc) (PDF version)
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NAG Library Manual

NAG Library Function Document

nag_dger (f16pmc)

 Contents

    1  Purpose
    7  Accuracy

1  Purpose

nag_dger (f16pmc) performs a rank-1 update on a real general matrix.

2  Specification

#include <nag.h>
#include <nagf16.h>
void  nag_dger (Nag_OrderType order, Nag_ConjType conj, Integer m, Integer n, double alpha, const double x[], Integer incx, const double y[], Integer incy, double beta, double a[], Integer pda, NagError *fail)

3  Description

nag_dger (f16pmc) performs the rank-1 update operation
AαxyT+βA,  
where A is an m by n real matrix, x is an m element real vector, y is an n-element real vector, and α and β are real scalars. If m or n is equal to zero or if β is equal to one and α is equal to zero, this function returns immediately.

4  References

Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001) Basic Linear Algebra Subprograms Technical (BLAST) Forum Standard University of Tennessee, Knoxville, Tennessee http://www.netlib.org/blas/blast-forum/blas-report.pdf

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 2.3.1.3 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:     conj Nag_ConjTypeInput
On entry: the argument conj is not referenced if x and y are real vectors. It is suggested that you set conj=Nag_NoConj where the elements yi are not conjugated.
Constraint: conj=Nag_NoConj.
3:     m IntegerInput
On entry: m, the number of rows of the matrix A.
Constraint: m0.
4:     n IntegerInput
On entry: n, the number of columns of the matrix A.
Constraint: n0.
5:     alpha doubleInput
On entry: the scalar α.
6:     x[dim] const doubleInput
Note: the dimension, dim, of the array x must be at least max1,1+n-1incx.
On entry: the n-element vector x.
If incx>0, xi must be stored in x[i-1×incx], for i=1,2,,m.
If incx<0, xi must be stored in x[m-i×incx], for i=1,2,,m.
Intermediate elements of x are not referenced. If m=0, x is not referenced and may be NULL.
7:     incx IntegerInput
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
8:     y[dim] const doubleInput
Note: the dimension, dim, of the array y must be at least max1,1+n-1incy.
On entry: the n-element vector y.
If incy>0, yi must be stored in y[i-1×incy], for i=1,2,,n.
If incy<0, yi must be stored in y[n-i×incy], for i=1,2,,n.
Intermediate elements of y are not referenced. If α=0.0 or n=0, y is not referenced and may be NULL.
9:     incy IntegerInput
On entry: the increment in the subscripts of y between successive elements of y.
Constraint: incy0.
10:   beta doubleInput
On entry: the scalar β.
11:   a[dim] doubleInput/Output
Note: the dimension, dim, of the array a must be at least
  • max1,pda×n when order=Nag_ColMajor;
  • max1,m×pda when order=Nag_RowMajor.
If order=Nag_ColMajor, Aij is stored in a[j-1×pda+i-1].
If order=Nag_RowMajor, Aij is stored in a[i-1×pda+j-1].
On entry: the m by n matrix A.
On exit: the updated matrix A.
12:   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, pdamax1,m;
  • if order=Nag_RowMajor, pdan.
13:   fail NagError *Input/Output
The NAG error argument (see Section 2.7 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_INT
On entry, incx=value.
Constraint: incx0.
On entry, incy=value.
Constraint: incy0.
On entry, m=value.
Constraint: m0.
On entry, n=value.
Constraint: n0.
NE_INT_2
On entry, pda=value, m=value.
Constraint: pdamax1,m.
On entry, pda=value and n=value.
Constraint: pdan.
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.
An unexpected error has been triggered by this function. Please contact NAG.
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

The BLAS standard requires accurate implementations which avoid unnecessary over/underflow (see Section 2.7 of Basic Linear Algebra Subprograms Technical (BLAST) Forum (2001)).

8  Parallelism and Performance

nag_dger (f16pmc) is not threaded in any implementation.

9  Further Comments

The argument conj is not referenced in this case where x and y are real vectors.

10  Example

Perform rank-1 update of real matrix A using vectors x and y:
A A - x yT ,  
where A is the 3 by 2 matrix given by
A = 3.0 2.0 3.0 4.0 5.0 9.0 ,  
x = 2.0,3.0,5.0T   and   y = 0.0,1.0,0.0T .  

10.1  Program Text

Program Text (f16pmce.c)

10.2  Program Data

Program Data (f16pmce.d)

10.3  Program Results

Program Results (f16pmce.r)


nag_dger (f16pmc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG Library Manual

© The Numerical Algorithms Group Ltd, Oxford, UK. 2016