nag_dger (f16pmc) (PDF version)
f16 Chapter Contents
f16 Chapter Introduction
NAG C 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
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

The BLAS Technical Forum Standard (2001)

5  Arguments

1:     orderNag_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 in the Essential Introduction for a more detailed explanation of the use of this argument.
Constraint: order=Nag_RowMajor or Nag_ColMajor.
2:     conjNag_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:     mIntegerInput
On entry: m, the number of rows of the matrix A.
Constraint: m0.
4:     nIntegerInput
On entry: n, the number of columns of the matrix A.
Constraint: n0.
5:     alphadoubleInput
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 vector x.
7:     incxIntegerInput
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 vector y.
9:     incyIntegerInput
On entry: the increment in the subscripts of y between successive elements of y.
Constraint: incy0.
10:   betadoubleInput
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:   pdaIntegerInput
On entry: the stride separating row or column elements (depending on the value of order) in the array a.
  • if order=Nag_ColMajor, pdamax1,m;
  • if order=Nag_RowMajor, pdan.
13:   failNagError *Input/Output
The NAG error argument (see Section 3.6 in the Essential Introduction).

6  Error Indicators and Warnings

Dynamic memory allocation failed.
On entry, argument value had an illegal value.
On entry, incx=value.
Constraint: incx0.
On entry, incy=value.
Constraint: incy0.
On entry, m=value.
Constraint: m0.
On entry, n=value.
Constraint: n0.
On entry, pda=value, m=value.
Constraint: pdamax1,m.
On entry, pda=value and n=value.
Constraint: pdan.
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.

7  Accuracy

The BLAS standard requires accurate implementations which avoid unnecessary over/underflow (see Section 2.7 of The BLAS Technical Forum Standard (2001)).

8  Further Comments

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

9  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 .

9.1  Program Text

Program Text (f16pmce.c)

9.2  Program Data

Program Data (f16pmce.d)

9.3  Program Results

Program Results (f16pmce.r)

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

© The Numerical Algorithms Group Ltd, Oxford, UK. 2012