How to save a variable from workspace into a .mat file, but the variable obtains value from a for loop?

I have this code and i want to save the variable x from workspace into a file clc;

clear; 
close all;
% Parameters
sampling_frequency = 1000;  % Sampling frequency in Hz
duration = 5;  % Duration of signal acquisition in seconds
num_samples = sampling_frequency * duration;
% Initialize variables
time = (0:num_samples-1) / sampling_frequency;
x = zeros(1, num_samples);
% Connect to Arduino 
a = arduino();
% Bandpass filter parameters
low_cutoff_frequency = 6;  % Low cutoff frequency in Hz
high_cutoff_frequency = 400;  % High cutoff frequency in Hz
% Design the bandpass filter
[b, a_filter] = butter(2, [low_cutoff_frequency, high_cutoff_frequency] / (sampling_frequency / 2), 'bandpass');                    %Normalized between [0 1]
% Plot for real-time visualization of raw signal
figure('Name', 'Real-Time Raw EMG Signal');
h_raw = plot(nan, nan); % Initialize plot with NaN
grid on;
title('Real-Time Raw EMG Signal');
xlabel('Time (s)');
ylabel('Voltage (V)');
xlim([0, duration]);  % Adjust xlim as needed
ylim([0, 5]);  % Adjust ylim according to expected voltage range
% Plot for real-time visualization of filtered signal
figure('Name', 'Real-Time Filtered EMG Signal');
h_filtered = plot(nan, nan); % Initialize plot with NaN
grid on;
title('Real-Time Filtered EMG Signal');
xlabel('Time (s)');
ylabel('Voltage (V)');
xlim([0, duration]);  % Adjust xlim as needed
ylim([0, 5]);  % Adjust ylim according to expected voltage range
% Start loop to acquire signal
for i = 1:num_samples
    % Read voltage
    raw_voltage = readVoltage(a, 'A0');
    
    % Store raw voltage
    x(i) = raw_voltage;
    
    % Apply bandpass filter to the signal up to current point if enough data points are collected
    if i >= 25  
        filtered_signal = filtfilt(b, a_filter, x(1:i));
        
        % Remove DC offset by subtracting the mean of the filtered signal
        filtered_signal = filtered_signal - mean(filtered_signal);
        
        % Update plot for filtered signal
        set(h_filtered, 'YData', filtered_signal, 'XData', time(1:i));
    end
    
    % Update plot for raw signal
    set(h_raw, 'YData', x(1:i), 'XData', time(1:i));
    
    drawnow;
    
end
save('EMG_data.mat', 'x',);

It doesn't create the .mat file and I suppose the problem is that i stop the iteration very early. But I want to save any values that are obtained until any iteration. How can I fix that?

Answer 1

[Animesh]

Hey @Iro Liontou,

To ensure that the variable "x" is saved to a MAT file even if the iteration is stopped early, you can use a "try-catch" block in MATLAB. Using this, regardless of whether the loop completes or is interrupted, the variable "x" will be saved.

try
    for i = 1:num_samples
        %code
    end
catch ME
    disp('Loop interrupted.');
    disp(ME.message);
end
save('EMG_data.mat', 'x');

You can refer the following MathWorks documentation for more information:

https://www.mathworks.com/help/matlab/ref/try.html

[Iro Liontou]

Great! I'll try it, thank you very much!