NAG C Library Function Document

nag_fft_init_trig (c06gzc)

1
Purpose

nag_fft_init_trig (c06gzc) calculates the trigonometric coefficients required for the computation of discrete Fourier transforms.

2
Specification

#include <nag.h>
#include <nagc06.h>
void  nag_fft_init_trig (Integer n, double trig[], NagError *fail)

3
Description

This is a utility function for use in conjunction with nag_fft_multiple_real (c06fpc) and nag_fft_multiple_hermitian (c06fqc). nag_fft_init_trig (c06gzc) initializes the array trig with trigonometric coefficients according to the value of n and must be called prior to the first call of one of the above listed functions.

4
References

None.

5
Arguments

1:     n IntegerInput
On entry: the value of n  in the Fourier transform function being called.
Constraint: n1 .
2:     trig[2×n] doubleOutput
On exit: the trigonometric coefficients are stored in trig.
3:     fail NagError *Input/Output
The NAG error argument (see Section 3.7 in How to Use the NAG Library and its Documentation).

6
Error Indicators and Warnings

NE_INT_ARG_LT
On entry, n=value.
Constraint: n1.

7
Accuracy

Exact.

8
Parallelism and Performance

nag_fft_init_trig (c06gzc) is not threaded in any implementation.

9
Further Comments

None.

10
Example

The program reads in 3 real data sequences and prints their discrete Fourier transforms in Hermitian format as calculated by nag_fft_multiple_real (c06fpc). A call is made to nag_fft_init_trig (c06gzc) to initialize the array trig prior to calling nag_fft_multiple_real (c06fpc). The transforms are then printed out in full complex form after a call to nag_multiple_hermitian_to_complex (c06gsc).

10.1
Program Text

Program Text (c06gzce.c)

10.2
Program Data

Program Data (c06gzce.d)

10.3
Program Results

Program Results (c06gzce.r)