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I want to find equation of this signal.

I plot this time series data and filter it with sSgolay filter. Now I want to get equation of this signal. Is this possible in matlab??

I have attached data of this plot with this post

Star Strider
on 15 Jul 2017

I am not certain what you intend by getting an equation for it.

You can filter out the noise to see the general trend:

fidi = fopen('data.txt','rt');

D = textscan(fidi, '%s%f', 'Delimiter','\t', 'CollectOutput',1);

t = datenum(D{1});

s = D{2};

Ts = mean(diff(t)); % Sampling Interval

Fs = 1/Ts; % Sampling Frequency

Fn = Fs/2; % Nyquist Frequency

L = numel(t); % Signal Length

sm = s-mean(s); % Subtract Mean To Make Amplitudes At Frequencies>0 More Prominent

FTs = fft(sm)/L; % Fourier Transform

Fv = linspace(0, 1, fix(L/2)+1)*Fn; % Frequency Vector

Iv = 1:length(Fv); % Index Vector

Phs = angle(FTs);

figure(1)

plot(Fv, abs(FTs(Iv))*2)

grid

xlabel('Frequency (Days^{-1})')

ylabel('Amplitude')

set(gca, 'XLim',[0 0.05])

Wp = [0.0045]/Fn; % Passband Frequencies (Normalised)

Ws = [0.0055]/Fn; % Stopband Frequencies (Normalised)

Rp = 10; % Passband Ripple (dB)

Rs = 50; % Stopband Ripple (dB)

[n,Ws] = cheb2ord(Wp,Ws,Rp,Rs); % Filter Order

[z,p,k] = cheby2(n,Rs,Ws); % Filter Design

[sosbp,gbp] = zp2sos(z,p,k); % Convert To Second-Order-Section For Stability

figure(2)

freqz(sosbp, 2^16, Fs) % Filter Bode Plot

s_filt = filtfilt(sosbp,gbp, s); % Filter Signal

figure(3)

plot(t, s, '-b')

hold on

plot(t, s_filt, '-r', 'LineWidth',1.5)

hold off

xlabel('Time (Days)')

ylabel('Amplitude')

legend('Original', 'Lowpass Filtered')

Star Strider
on 20 Jul 2017

@Muhammad Usman Saleem —

The point of my comment is that the neural network did not work.

I encourage you either to thoroughly study meteorological models and their complexity, or to abandon this idea and consider a more tractable problem.

Star Strider
on 24 Jul 2017

As always, my pleasure!

If my Answer helped solve your problem, please Accept it.

Opportunities for recent engineering grads.

Apply Today
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