How to get equation of signal in matlab

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Muhammad Usman Saleem 2017-7-15

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https://ww2.mathworks.cn/matlabcentral/answers/348847-how-to-get-equation-of-signal-in-matlab

评论： Star Strider 2017-7-24

采纳的回答： Star Strider

data.txt

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

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Muhammad Usman Saleem 2017-7-20

@Grej Thanks for your reply. I have not expertise in neural network. So I not know whether this network has created for such meteorological problems. In matlab I know there are some models like AR, ARMA which simulate the data set then forecast it. I tried them alot but unable to fit them due to lacking in expertise.

How can I forecast snow for one day ahead using this time series data set?

Thanks

Greg Heath 2017-7-20

在 MATLAB Online 中打开

 help NARNET
 doc NARNET
 help NNCORR
 doc NNCORR
 greg NARNET

Hope this helps.

Greg

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Star Strider 2017-7-15

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https://ww2.mathworks.cn/matlabcentral/answers/348847-how-to-get-equation-of-signal-in-matlab#answer_274268

在 MATLAB Online 中打开

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')