NAG FL Interface
f16jtf (zamin_​val)

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1 Purpose

f16jtf computes, with respect to absolute value, the smallest component of a complex vector, along with the index of that component.

2 Specification

Fortran Interface
Subroutine f16jtf ( n, x, incx, k, r)
Integer, Intent (In) :: n, incx
Integer, Intent (Out) :: k
Real (Kind=nag_wp), Intent (Out) :: r
Complex (Kind=nag_wp), Intent (In) :: x(1+(n-1)*ABS(incx))
C Header Interface
#include <nag.h>
void  f16jtf_ (const Integer *n, const Complex x[], const Integer *incx, Integer *k, double *r)
The routine may be called by the names f16jtf, nagf_blast_zamin_val or its BLAST name blas_zamin_val.

3 Description

f16jtf computes, with respect to absolute value, the smallest component, r, of an n-element complex vector x, and determines the smallest index, k, such that
r=|Rexk|+|Imxk|=minj|Rexj|+|Imxj|.  

4 References

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

5 Arguments

1: n Integer Input
On entry: n, the number of elements in x.
2: x(1+(n-1)×|incx|) Complex (Kind=nag_wp) array Input
On entry: the n-element vector x.
If incx>0, xi must be stored in x((i-1)×incx+1), for i=1,2,,n.
If incx<0, xi must be stored in x((n-i)×|incx|+1), for i=1,2,,n.
Intermediate elements of x are not referenced. If n=0, x is not referenced.
3: incx Integer Input
On entry: the increment in the subscripts of x between successive elements of x.
Constraint: incx0.
4: k Integer Output
On exit: k, the index, from the set {1,2,,n} , of the smallest component of x with respect to absolute value. If n0 on input then k is returned as 0.
5: r Real (Kind=nag_wp) Output
On exit: r, the smallest component of x with respect to absolute value. If n0 on input then r is returned as 0.0.

6 Error Indicators and Warnings

If incx=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

Background information to multithreading can be found in the Multithreading documentation.
f16jtf is not threaded in any implementation.

9 Further Comments

None.

10 Example

This example computes the smallest component with respect to absolute value and index of that component for the vector
x= (-4+2.1i,3.7+4.5i,-6+1.2i) T .  

10.1 Program Text

Program Text (f16jtfe.f90)

10.2 Program Data

Program Data (f16jtfe.d)

10.3 Program Results

Program Results (f16jtfe.r)