NAG Library Routine Document

f16gcf  (zaxpby)

 Contents

    1  Purpose
    7  Accuracy

1
Purpose

f16gcf (blas_zaxpby) computes the sum of two scaled vectors, for complex scalars and vectors.

2
Specification

Fortran Interface
Subroutine f16gcf ( n, alpha, x, incx, beta, y, incy)
Integer, Intent (In):: n, incx, incy
Complex (Kind=nag_wp), Intent (In):: alpha, x(1+(n-1)*ABS(incx)), beta
Complex (Kind=nag_wp), Intent (Inout):: y(1+(n-1)*ABS(incy))
C Header Interface
#include nagmk26.h
void  f16gcf_ ( const Integer *n, const Complex *alpha, const Complex x[], const Integer *incx, const Complex *beta, Complex y[], const Integer *incy)
The routine may be called by its BLAST name blas_zaxpby.

3
Description

f16gcf (blas_zaxpby) performs the operation
y αx+βy,  
where x and y are n-element complex vectors, and α and β are complex scalars. If n is less than or equal to zero, or if α is equal to zero and β is equal to 1, this routine 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:     n – IntegerInput
On entry: n, the number of elements in x and y.
2:     alpha – Complex (Kind=nag_wp)Input
On entry: the scalar α.
3:     x1+n-1×incx – Complex (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. If n=0, x is not referenced.
4:     incx – IntegerInput
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
5:     beta – Complex (Kind=nag_wp)Input
On entry: the scalar β.
6:     y1+n-1×incy – Complex (Kind=nag_wp) arrayInput/Output
On entry: the n-element vector y.
If incy>0, yi must be stored in yi-1×incy+1, for i=1,2,,n.
If incy<0, yi must be stored in yn-i×incy+1, for i=1,2,,n.
Intermediate elements of y are not referenced.
On exit: the updated vector y stored in the array elements used to supply the original vector y.
Intermediate elements of y are unchanged.
7:     incy – IntegerInput
On entry: the increment in the subscripts of y between successive elements of y.
Constraint: incy0.

6
Error Indicators and Warnings

If incx=0 or incy=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

f16gcf (blas_zaxpby) 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 routine. Please also consult the Users' Note for your implementation for any additional implementation-specific information.

9
Further Comments

None.

10
Example

This example computes the result of a scaled vector accumulation for
α=3+2i,   x = -6+1.2i,3.7+4.5i,-4+2.1iT , β=-i,   y = -5.1,6.4-5i,-3-2.4iT .  
x and y are stored in reverse order.

10.1
Program Text

Program Text (f16gcfe.f90)

10.2
Program Data

Program Data (f16gcfe.d)

10.3
Program Results

Program Results (f16gcfe.r)

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