F16EHF (BLAS_DWAXPBY) (PDF version)
F16 Chapter Contents
F16 Chapter Introduction
NAG Library Manual

NAG Library Routine Document

F16EHF (BLAS_DWAXPBY)

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

1  Purpose

F16EHF (BLAS_DWAXPBY) computes the sum of two scaled vectors, preserving input, for real scalars and vectors.

2  Specification

SUBROUTINE F16EHF ( N, ALPHA, X, INCX, BETA, Y, INCY, W, INCW)
INTEGER  N, INCX, INCY, INCW
REAL (KIND=nag_wp)  ALPHA, X(1+(N-1)*ABS(INCX)), BETA, Y(1+(N-1)*ABS(INCY)), W(1+(N-1)*ABS(INCW))
The routine may be called by its BLAST name blas_dwaxpby.

3  Description

F16EHF (BLAS_DWAXPBY) performs the operation
w αx+βy,  
where x and y are n-element real vectors, and α and β are real scalars.

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  Parameters

1:     N – INTEGERInput
On entry: n, the number of elements in x, y and w.
2:     ALPHA – REAL (KIND=nag_wp)Input
On entry: the scalar α.
3:     X1+N-1×INCX – REAL (KIND=nag_wp) arrayInput
On entry: the n-element vector x.
If INCX>0, xi must be stored in Xi-1×INCX+1, for i=1,2,,N.
If INCX<0, xi must be stored in XN-i×INCX-1, for i=1,2,,N.
Intermediate elements of X are not referenced.
4:     INCX – INTEGERInput
On entry: the increment in the subscripts of X between successive elements of x.
Constraint: INCX0.
5:     BETA – REAL (KIND=nag_wp)Input
On entry: the scalar β.
6:     Y1+N-1×INCY – REAL (KIND=nag_wp) arrayInput
On entry: the n-element vector y.
If INCY>0, yi must be stored in Y1+i-1×INCY, for i=1,2,,N.
If INCY<0, yi must be stored in Y1-N-i×INCY, for i=1,2,,N.
Intermediate elements of Y are not referenced.
7:     INCY – INTEGERInput
On entry: the increment in the subscripts of Y between successive elements of y.
Constraint: INCY0.
8:     W1+N-1×INCW – REAL (KIND=nag_wp) arrayOutput
On exit: the n-element vector w.
If INCW>0, wi is in W1+i-1×INCW , for i=1,2,,N.
If INCW<0, wi is in W1+N-i×INCW , for i=1,2,,N.
Intermediate elements of W are not referenced.
9:     INCW – INTEGERInput
On entry: the increment in the subscripts of W between successive elements of w.
Constraint: INCW0.

6  Error Indicators and Warnings

If INCX=0 or INCY=0 or INCW=0, an error message is printed and program execution is terminated.

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

Not applicable.

9  Further Comments

None.

10  Example

This example computes the result of a scaled vector accumulation for
α=3,   x = -4,2.1,3.7,4.5,-6T , β=-1,   y = -3,-2.4,6.4,-5,-5.1T .  

10.1  Program Text

Program Text (f16ehfe.f90)

10.2  Program Data

Program Data (f16ehfe.d)

10.3  Program Results

Program Results (f16ehfe.r)


F16EHF (BLAS_DWAXPBY) (PDF version)
F16 Chapter Contents
F16 Chapter Introduction
NAG Library Manual

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