How to obtain an array of maxima from a moving maximum?

I would like to get the moving maximum of an array, however I would like the output array to be the same length as the input array and also only place the maximum value for any given window in the same index it was found in the input array. If the next window has the same maximum data point, I would like to input a zero for that index in the output array. An example is below:

A = [4 8 6 1 2 3 1 9 4 5]; % Input data array

windowLength = 3; % Window length for the moving maximum.

The desired output from the example above is:

M = [0 8 6 0 0 3 0 9 0 0];

I tried using both dsp.MovingMaximum and movmax but neither the desired output array.

Answer 1

[Image Analyst]

They don't work because you're wanting a specialized operation. Here is a way that works:

A = [4 8 6 1 2 3 1 9 4 5]; % Input data array
output = zeros(1, length(A));
windowLength = 3; % Window length for the moving maximum.
for k = 1 : length(A) - windowLength + 1
  thisWindow = A(k : k + windowLength - 1)
  windowMax = max(thisWindow)
  for k2 = k : k + windowLength - 1
    if thisWindow(k2-k+1) == windowMax
      output(k2) = A(k2);
    end
  end
end
output % Show in command window.

[JakeE10]

That works well to achieve the desired output, however it runs slowly for large arrays (i.e. 20E6 or more points). Is there an easy was to speed this process up? I know parfor loops will not work because of the indexing that goes on when searching the array, but I was not sure if there are other useful tools I do not know about within MATLAB.

Thank you.

Answer 2

[Akshay Dighe]

Hi,

What does the movmax function matlab actually does?

I am not understanding why it is used, please help!

[Image Analyst]

movmax() slides a window along the vector of numbers and makes an output vector with the max of the values in the window. For example when the max is up against the left edge of the array and the window is 3 elements wide, it will make the first value of the output vector equal to the max of the first three values. The second output value is the max of the values at indexes 2, 3, and 4.

[Akshay Dighe]

Thank you for the answer!

I have as question given by my professor. But I am unable to understand it and do the coding. I understood the theory but to convert it into the code seems difficult.

Can you help me out?

Here is the question

[Akshay Dighe]

Other question