# 2.1.22.2.1.32 fft_fft_real

## Description

calculates the discrete Fourier transform or inverse Fourier transform of a sequence of iSize real data values. For forward FT, the output is in Hermitian form; For backward FT, the input sequence is in Hermitian form.

## Syntax

int fft_fft_real( int iSize, double * vSig, FFT_SIGN iSign = FFT_FORWARD )

## Parameters

iSize
[input] the number of data values in the sequence.
vSig
[Modify] Input data array for transformation, also used for output the discrete Fourier transform stored in Hermitian form.
iSign
[input] the transformation to carry out
= FFT_FORWARD: FFT (by default)
= FFT_BACKWARD: IFFT.

## Return

Returns 0 for success or error codes for failure.

## Examples

EX1

//Assume the current Worksheet has 4 columns. The first column contains 7 data. This piece
//of code reads in a sequence of real data values from the first column, and prints
//their discrete Fourier transform (as computed by fft_fft_real) into the second and
//the third column, after    expanding it from Hermitian form into a full complex sequence.
//It also performs an inverse    transform to obtain the original data in the fourth column.

#include <..\originlab\fft.h>
void TEST_fft_fft_real()
{
int n = 7, j, success, n2, nj;
//Attach 4 Datasets to these 4 columns
Worksheet wks = Project.ActiveLayer();
if(wks)
{
Dataset xx(wks, 0);
Dataset aa(wks, 1);
aa.SetSize(n);
Dataset bb(wks, 2);
bb.SetSize(n);
Dataset cc(wks, 3);
cc.SetSize(n);

vector x = xx;

///FT
success = fft_fft_real(n, x);

//output the result into worksheet.
if(success == 0)
{
aa = x;
bb = 0.0;
n2 = (n-1)/2;
for (j = 1; j<=n2; j++)
{
nj = n - j;
aa[j] = x[j];
aa[nj] = x[j];
bb[j] = x[nj];
bb[nj] = -x[nj];
}
if (n % 2==0)
{
aa[n2+1] = x[n2+1];
bb[n2+1] = 0.0;
}
}

///IFT
success = fft_fft_real(n, x, FFT_BACKWARD);

//output the result into worksheet.
cc = x;
}
}