NAG Toolbox: nag_blast_daxpby (f16ec)

Purpose

Syntax

Description

References

Parameters

Compulsory Input Parameters

1:     $\mathrm{n}$ – int64int32nag_int scalar

$n$, the number of elements in $x$ and $y$.

2:     $\mathrm{alpha}$ – double scalar

The scalar $\alpha$.

3:     $\mathrm{x}\left(1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incx}\right|\right)$ – double array

The $n$-element vector $x$.

If $\mathbf{incx}>0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(\left(\mathit{i}-1\right)\times \left|\mathbf{incx}\right|+1\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

If $\mathbf{incx}<0$, $x_{\mathit{i}}$ must be stored in $\mathbf{x}\left(\left(\mathbf{n}-\mathit{i}\right)\times \left|\mathbf{incx}\right|-1\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Intermediate elements of x are not referenced.

4:     $\mathrm{incx}$ – int64int32nag_int scalar

The increment in the subscripts of x between successive elements of $x$.

Constraint: $\mathbf{incx}\ne 0$.

5:     $\mathrm{beta}$ – double scalar

The scalar $\beta$.

6:     $\mathrm{y}\left(1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incy}\right|\right)$ – double array

The $n$-element vector $y$.

If $\mathbf{incy}>0$, $y_{\mathit{i}}$ must be stored in $\mathbf{y}\left(1+\left(\mathit{i}-1\right)\times \mathbf{incy}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

If $\mathbf{incy}<0$, $y_{\mathit{i}}$ must be stored in $\mathbf{y}\left(1-\left(\mathbf{n}-\mathit{i}\right)\times \mathbf{incy}\right)$, for $\mathit{i}=1,2,\dots ,\mathbf{n}$.

Intermediate elements of y are not referenced.

7:     $\mathrm{incy}$ – int64int32nag_int scalar

The increment in the subscripts of y between successive elements of $y$.

Constraint: $\mathbf{incy}\ne 0$.

Optional Input Parameters

None.

Output Parameters

1:     $\mathrm{y}\left(1+\left(\mathbf{n}-1\right)\times \left|\mathbf{incy}\right|\right)$ – double array

The updated vector $y$ stored in the array elements used to supply the original vector $y$.

Intermediate elements of y are unchanged.

Error Indicators and Warnings

Accuracy

Further Comments

Example

Open in the MATLAB editor: f16ec_example

function f16ec_example


fprintf('f16ec example results\n\n');

% real vectors x and y;
n = int64(5);
x = [-4    2.1    3.7    4.5   -6.0];
y = [-3   -2.4    6.4   -5.0   -5.1];

% z = 3x - y;
alpha = 3;
beta = -1;

incx = int64(1);
incy = incx;

[z] = f16ec(n, alpha, x, incx, beta, y, incy);

fprintf('x = ');
fprintf('%5.1f',x);
fprintf('\ny = ');
fprintf('%5.1f',y);
fprintf('\n%4.1f x %+4.1f y = ',alpha,beta);
fprintf('%7.1f',z);
fprintf('\n');

f16ec example results

x =  -4.0  2.1  3.7  4.5 -6.0
y =  -3.0 -2.4  6.4 -5.0 -5.1
 3.0 x -1.0 y =    -9.0    8.7    4.7   18.5  -12.9