MATLAB: Zero-crossing of every column of a matrix

zero crossing

I have a 351×117 matrix. I need to compute the zero-crossing of every column of the matrix, in order to obtain the average max and min amplitude of every individual wave within each column.

I believe this would be a loop problem, or perhaps this might require a User-defined-function? Any help on how to get started?

Best Answer

If you want the maximum and minimum amplitudes (and you have R2017b or later releases), use the islocalmax and islocalmin funcitons. Also, if you have the Signal Processing Toolbox, you can use findpeaks on the original and negative (to find the minima) versions of your signal, however it requires a loop for matrices because it only handles vectors.

There is no need to find the zero-crossings then. (However if you still need to find them, doing so is relatively straightforward.)

Related Solutions

MATLAB: Finding zeroes of data

This is a routine I use to find as many zero-crossings in data as may exist. It interpolates or extrapolates from the points it identifies near the zero crossings to closely (linearly) approximate the actual zero crossings:

x = linspace(0,10*pi,1E+5);                                             % Create Data

y = sin(10*pi*x.*cos(10*x).^2);                                         % Create Data
zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
dy = zci(y);                                                            % Indices of Approximate Zero-Crossings
for k1 = 1:size(dy,1)-1
    b = [[1;1] [x(dy(k1)); x(dy(k1)+1)]]\[y(dy(k1)); y(dy(k1)+1)];      % Linear Fit Near Zero-Crossings
    x0(k1) = -b(1)/b(2);                                                % Interpolate ‘Exact’ Zero Crossing
    mb(:,k1) = b;                                                       % Store Parameter Estimates (Optional)
end

It should work for your data without much, if any, modification. The zero-crossings are in the ‘x0’ vector.

MATLAB: Failed to create signal form successive values

You can do it without the loop:

zci = @(v) find(v(:).*circshift(v(:), [-1 0]) <= 0);                    % Returns Approximate Zero-Crossing Indices Of Argument Vector
MACD = rand(1, 25)-0.5;                                                 % Create ‘MACD’ Data
zx = zci(MACD);                                                         % Find Zero-Crossings
zx = zx(1:end-1);                                                       % Eliminate Wrap-Around ‘End Effect’
sx = sign(MACD(zx+1));                                                  % Set Signs Of Zero-Crossings
s = zeros(size(MACD));                                                  % Define ‘s’
s(zx+1) = sx;                                                           % Insert Sign Vector Into ‘s’

My code uses the ‘zci’ anonymous function to return the zero-crossing indices of your ‘MACD’ vector, then assigns the sign by looking at the next value in the vector in the ‘sx’ vector. It then creates ‘s’ and assigns ‘sx’ to the appropriate positions in it to create the desired output for ‘s’.

Best Answer

Related Solutions

MATLAB: Finding zeroes of data

MATLAB: Failed to create signal form successive values

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