The issue is in line 52, where matlab states "Index exceeds the number of array elements. Index must not exceed 1."

This algorithm is made to produce a magnitude, phase and frequency of 360 sine waves.

%% part one declearing variables and setting loop 
load('mlab2_timeandrawdata.mat')%loads file 
clearvars -except ex2data %clear all variables of data except the ex2data file 

figure
T = ex2data(1,:); %listing all the data points in the first row of the 

%% loop starting 
for i = 2:1:10 %declearing variable i to be sampled at interval of 1, from 2 to 361
    
    y = ex2data(i,:);%delcearing all data from the remaining rows 2-361
    signal = y; %adds the two variable y and t to get the signal wave 
    plot(T,y,'r-') %plotting y and x red with dash line
    axis ([0 2 -83 83]) %sets the limit for the 
    hold on; %adding below 
    plot(T, zeros(1,length(T)), 'k-'); %plotting zero line 
    
    
    %% find next point after zero crossing
    sigPos = logical(signal>0); % find all positive points
    cross = sigPos - circshift(sigPos,1); % find changeover points 
    plot(T(logical(cross)), signal(logical(cross)), 'bo');
    
    %% assume straight line approximation between adjacent points
    crossInd = find(cross); % x indices of cross points
    nCross = length(crossInd); % number of cross points found
    x0 = NaN(1,nCross); % vector of x-values for cross points
    
    for aa = 2:nCross%from 2 to ncross
        thisCross = crossInd(aa);%to track the variables 
        
        %% interpolate to get x coordinate of approx 0
        x1 = thisCross-1; % before-crossing x-value
        x2 = thisCross; % after-crossing x-value
        y1 = signal (thisCross-1); % before-crossing y-value
        y2 = signal(thisCross); % after-crossing y-value
        
        ratio = (0-y1) / (y2-y1); % interpolate between points to find 0
        x0(aa) = T(x1) + (ratio*(T(x2)-T(x1))); % estimate of x-value
        
    end
    
    % add to plot the zero line of function
    plot(x0, zeros(1,nCross), 'go');
    
    %% to avoid the outcome of have a NaN 
    if (isnan(x0(1)))
        x0 = x0(2:length(x0));
    end
    
    %% set as a function of i
    P = x0(3)-x0(1);% firs period given the two points on wave first and third point
    d = x0(5)-x0(1);% second period with points 5 and 1 on zero line 
    PS(i) = d/P * 360; % Phase in radians, of the function of i  to tracked
    f(i) = 1/abs(x0(5)-x0(1)); %frequency of the function of i  to tracked
    M(i) = max(y);%sotres the magnitude
    
end

%% stores variables in a matrix 
z = [M;f;PS]; %stores the matrix for M, f, and PS in column

[KALYAN ACHARJYA]

Please attach 'mlab2_timeandrawdata.mat' file.

Answer 1

[Chetan]

Hello @Justin Ramnarine ,

I understand you're working on signal processing in MATLAB and facing an "Index exceeds the number of array elements" error at line 52.

This typically occurs when you're trying to access an element beyond the size of the array.

In the code, you're trying to access the 3rd and 5th elements of the `x0` array:

P = x0(3)-x0(1);
d = x0(5)-x0(1);

The error likely arises because `x0` may not have enough elements, especially during the initial iterations of your loop.

To resolve this, add a condition to check if `x0` has sufficient elements before accessing them:

if length(x0) >= 5
    P = x0(3)-x0(1);
    d = x0(5)-x0(1);
    PS(i) = d/P * 360;
    f(i) = 1/abs(x0(5)-x0(1));
    M(i) = max(y);
    

This ensures you only access the 3rd and 5th elements if they exist.

For more details on array indexing in MATLAB, refer to the following MathWorks Documentation https://www.mathworks.com/help/matlab/math/array-indexing.html

A more specific solution might require additional information about the data and the issues you're encountering.

I hope this helps!