*Documentation for ***nuft1**

(SPASS).
## Non uniform Fourier Transform with linear interpolation

### Description

The function `nuft1`

computes the Fourier transform of a non uniform signal for some given frequencies using linear interpolation to compute a continuous equivalent of the sampled signal.
The optional argument `lsig`

allows to choose between a no-signal (signal is supposed to be zero before the sampling of the first sample) and a no-activity (the previous signal is supposed to the same as the first sample) assumption.

### Usage

ft = nuft1(nu,f)
ft = nuft1(nu,f,'no-signal')
ft = nuft1(nu,f,'no-activity')

### Arguments

`nu` |
Input signal. Non Uniform signal. |

`f` |
Frequencies. Vector. |

`lsig` |
Choice of left data. String among 'no-signal' and 'no-activity'. *Optional,* default='no-signal'. |

### Values

### See Also

- nuft (Non uniform Fourier Transform (generic function))
- nuft0 (Non uniform Fourier Transform with zeroth order interpolation)
- nuftnn (Non uniform Fourier Transform with nearest neighbor interpolation)

### Example

% Creation of a non uniform signal
f = 1; % signal frequency
t = 10/f; % signal duration
fs = 1000; % sampling frequency
ts = 1/fs; % sampling time
t0 = 1.; % initial time
times = t0+(0:ts:t); % time samples
a = 0.45; % signal amplitude
ampl = a*sin(2*pi*f*times)+a*sin(4*2*pi*f*times)+0.9; % amplitudes
u = uinit(ampl,ts,t0);
% Level crossing
levels = [.1 .4 .7 1.1 1.4 1.7];
nu = levelcross(u,levels);
% Frequencies and transform
f = 0:.02:6;
ft = nuft1(nu,f);
% Plot result
figure(1)
plot(f,abs(ft.ampl),'k','LineWidth',1)