MATLAB: How do i plot maximum values

if loop

I am writing a function to plot all the maximum values of a 1D matrix on a graph. When i click 'Run', no figure shows up and the command window just displays all the figures of the 1D matrix. what am i doing wrong?

Best Answer

You weren't actually calling the function. Secondly, the function had no input argument for threshold so I've included that. I also removed the loop as it simplifies the code and makes it more efficient.

ECG = load('ECG.csv');
f_s = 350; %Frequency of ECG [Hz]
Time = (0:length(ECG)-1)/f_s; %Number of samples divided by frquency
Amp = ECG(:,1); %ECG Amplitude
threshold = 100;
figure(), plot(Time,Amp,'b-') % I've pulled this out of the function
[Time_peak, Amp_peak] = findLocalMaxThreshold(Time,Amp,threshold)
hold on; plot(Time_peak, Amp_peak, '*r')
function [xp,yp] = findLocalMaxThreshold(x,y,threshold)
    idx = find(y(2:end-1) > (y(1:end-2)) & y(2:end-1) > y(3:end) & y(2:end-1) > threshold ) + 1;
    xp = x(idx);
    yp = y(idx);
end

Related Solutions

MATLAB: Findpeaks function won’t plot all peaks.

Thje last R-wave is not actually a peak as findpeaks defines it.

It is necessary to get creative in order to isolate and define it:

ECG = load('ECG.csv')
Frequency = 350; %Frequency of ECG [Hz]
Time = (0:length(ECG)-1)/Frequency; %Number of samples divided by frquency
Amp = ECG(:,1); %ECG Amplitude
figure
% plot(Time,Amp)
findpeaks(Amp,Time,'MinPeakProminence',100);
[pks,locs] = findpeaks(Amp,'MinPeakProminence',100);                % Return Indices Instead of Times
ofst = locs(end)+1;                                                 % Last Peak ‘loc’ + 1
[Rwaves,idx] = max(Amp(ofst:end));                                  % Maximum Of Remaining Segment Of ‘Amp’
meanCycle = mean(diff(Time(locs)));
BPM = 60/meanCycle;
fprintf('%.2f\n', BPM)
figure
plot(Time,Amp)
hold on
plot(Time(locs), Amp(locs), '^r', 'MarkerFaceColor','r')            % Plot Peaks That ‘findpeaks’ Returns
plot(Time(idx+ofst), Rwaves, 'pr', 'MarkerFaceColor','r')           % Plot Last Incomplete Peak
hold off

Producing:

1Findpeaks function won't plot all peaks - 2020 01 06.png

With the last ‘peak’ plotted with a pentagram.

MATLAB: I have a signal with many frequencies. how to find this frequencies and reconstruct the signal from these frequencies

I think this should work for you:

ffty = fft(y);
P2 = abs(ffty/length(ffty));
P1 = P2(1:ceil(length(y)/2)); 
P1(2:end-1) = 2*P1(2:end-1);
[amp,locs] = findpeaks(P1); 
freqs = (locs-1)/t(end); 
signal_1=0; 
for n=1:length(freqs) 
    signal_1 = (signal_1+amp(n)*sin(2*pi*freqs(n)*t)); 
end
hold on;
plot(smooth(signal_1));
plot(y,'b');

Here, P2 is the two-sided spectrum and P1 is the single-sided spectrum.

A two-sided power spectrum displays half the energy at the positive frequency and half the energy at the negative frequency. Therefore, to convert a two-sided spectrum to a single-sided spectrum, you discard the second half of the array and multiply every point except for DC by two.

Also, while regenerating the signal in the "for" loop, you need to take the amplitude of corresponding frequencies into consideration. Hence, you need the first output "amp" of "findpeaks".

You can also eliminate the "for" loop by using vectorization:

    signal_1=sum(amp'.*(sin(2*pi*freqs'*t)));

Best Answer

Related Solutions

MATLAB: Findpeaks function won’t plot all peaks.

MATLAB: I have a signal with many frequencies. how to find this frequencies and reconstruct the signal from these frequencies

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