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NAG Toolbox: nag_sum_fft_complex_1d_multi_row (c06pr)
Purpose
nag_sum_fft_complex_1d_multi_row (c06pr) computes the discrete Fourier transforms of sequences, each containing complex data values.
Syntax
Description
Given
sequences of
complex data values
, for
and
,
nag_sum_fft_complex_1d_multi_row (c06pr) simultaneously calculates the (
forward or
backward) discrete Fourier transforms of all the sequences defined by
(Note the scale factor
in this definition.) The minus sign is taken in the argument of the exponential within the summation when the forward transform is required, and the plus sign is taken when the backward transform is required.
A call of nag_sum_fft_complex_1d_multi_row (c06pr) with followed by a call with will restore the original data.
The function uses a variant of the fast Fourier transform (FFT) algorithm (see
Brigham (1974)) known as the Stockham self-sorting algorithm, which is described in
Temperton (1983). Special code is provided for the factors
,
,
and
.
References
Brigham E O (1974) The Fast Fourier Transform Prentice–Hall
Temperton C (1983) Self-sorting mixed-radix fast Fourier transforms J. Comput. Phys. 52 1–23
Parameters
Compulsory Input Parameters
- 1:
– string (length ≥ 1)
-
If the forward transform as defined in
Description is to be computed, then
direct must be set equal to 'F'.
If the backward transform is to be computed then
direct must be set equal to 'B'.
Constraint:
or .
- 2:
– int64int32nag_int scalar
-
, the number of sequences to be transformed.
Constraint:
.
- 3:
– int64int32nag_int scalar
-
, the number of complex values in each sequence.
Constraint:
.
- 4:
– complex array
-
The complex data must be stored in
x as if in a two-dimensional array of dimension
; each of the
sequences is stored in a
row of each array.
In other words, if the elements of the
th sequence to be transformed are denoted by
, for
, then
must contain
.
Optional Input Parameters
None.
Output Parameters
- 1:
– complex array
-
Stores the complex transforms.
- 2:
– int64int32nag_int scalar
unless the function detects an error (see
Error Indicators and Warnings).
Error Indicators and Warnings
Errors or warnings detected by the function:
-
-
-
-
-
-
On entry, | or . |
-
-
An unexpected error has occurred in an internal call. Check all function calls and array dimensions. Seek expert help.
-
An unexpected error has been triggered by this routine. Please
contact
NAG.
-
Your licence key may have expired or may not have been installed correctly.
-
Dynamic memory allocation failed.
Accuracy
Some indication of accuracy can be obtained by performing a subsequent inverse transform and comparing the results with the original sequence (in exact arithmetic they would be identical).
Further Comments
The time taken by nag_sum_fft_complex_1d_multi_row (c06pr) is approximately proportional to , but also depends on the factors of . nag_sum_fft_complex_1d_multi_row (c06pr) is fastest if the only prime factors of are , and , and is particularly slow if is a large prime, or has large prime factors.
Example
This example reads in sequences of complex data values and prints their discrete Fourier transforms (as computed by nag_sum_fft_complex_1d_multi_row (c06pr) with ). Inverse transforms are then calculated using nag_sum_fft_complex_1d_multi_row (c06pr) with and printed out, showing that the original sequences are restored.
Open in the MATLAB editor:
c06pr_example
function c06pr_example
fprintf('c06pr example results\n\n');
m = int64(3);
n = int64(6);
zr = [0.3854 0.6772 0.1138 0.6751 0.6362 0.1424;
0.9172 0.0644 0.6037 0.6430 0.0428 0.4815;
0.1156 0.0685 0.2060 0.8630 0.6967 0.2792];
zi = [0.5417 0.2983 0.1181 0.7255 0.8638 0.8723;
0.9089 0.3118 0.3465 0.6198 0.2668 0.1614;
0.6214 0.8681 0.7060 0.8652 0.9190 0.3355];
z = zr + i*zi;
title = 'Original sequences:';
[ifail] = x04da('General','Non-unit', z, title);
direct = 'F';
[zt, ifail] = c06pr(direct, m, n, z);
disp(' ');
title = 'Discrete Fourier Transforms:';
[ifail] = x04da('General','Non-unit', zt, title);
direct = 'B';
[zr, ifail] = c06pr(direct, m, n, zt);
disp(' ');
title = 'Original data as restored by inverse transform';
[ifail] = x04da('General','Non-unit', zr, title);
c06pr example results
Original sequences:
1 2 3 4 5 6
1 0.3854 0.6772 0.1138 0.6751 0.6362 0.1424
0.5417 0.2983 0.1181 0.7255 0.8638 0.8723
2 0.9172 0.0644 0.6037 0.6430 0.0428 0.4815
0.9089 0.3118 0.3465 0.6198 0.2668 0.1614
3 0.1156 0.0685 0.2060 0.8630 0.6967 0.2792
0.6214 0.8681 0.7060 0.8652 0.9190 0.3355
Discrete Fourier Transforms:
1 2 3 4 5 6
1 1.0737 -0.5706 0.1733 -0.1467 0.0518 0.3625
1.3961 -0.0409 -0.2958 -0.1521 0.4517 -0.0321
2 1.1237 0.1728 0.4185 0.1530 0.3686 0.0101
1.0677 0.0386 0.7481 0.1752 0.0565 0.1403
3 0.9100 -0.3054 0.4079 -0.0785 -0.1193 -0.5314
1.7617 0.0624 -0.0695 0.0725 0.1285 -0.4335
Original data as restored by inverse transform
1 2 3 4 5 6
1 0.3854 0.6772 0.1138 0.6751 0.6362 0.1424
0.5417 0.2983 0.1181 0.7255 0.8638 0.8723
2 0.9172 0.0644 0.6037 0.6430 0.0428 0.4815
0.9089 0.3118 0.3465 0.6198 0.2668 0.1614
3 0.1156 0.0685 0.2060 0.8630 0.6967 0.2792
0.6214 0.8681 0.7060 0.8652 0.9190 0.3355
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