spectral interpolation of the function in matlab

Hi,

I wonder if someone can give me example of spectral interpolation of the function.

funtioncs: fft, fftshift, or any other

Answer 1

[Wayne King]

Hi Feruz, just pad the fft(), that interpolates the DFT.

Fs = 1024;
t = 0:1/Fs:(1000*(1/1024))-(1/1024);
x = cos(2*pi*100*t)+randn(size(t));
xdft = fft(x);
plot(abs(xdft));

% now pad to 1024 to interpolate at 1 Hz spacing
xdft1 = fft(x,1024);
figure;
plot(abs(xdft1));

Look how much narrower the line component shows up in the latter

[Feruz]

Hi Wayne,

This is my code:

m = 4;

N = 2^m;

L = N;

M = 10;

j = 0:N-1;

x = j*L/N;

f = exp(-M*(j/L-0.3).^2);

z = fft(f,400);

figure;

plot(abs(z));

%z = fftshift(z);

figure;

plot(f);

But look at the plot, shouldn't be my interpolation close to the function?

[Greg Heath]

f is a bad choice for. a function. Use it for frequency.

f is complex. Either make it real or plot ampliitude and phase

Do not plot vs index. Plot f vs time and z vs frequency

Hope this helps.

Greg