How can I leave only the 10 largest elements of a matrix?

I would like to make the remainder of the magnitude matrix zero except for the 10 largest values.

The code is shown below.

while hasFrame(vidReader)    
  Fr2 = rgb2gray(readFrame(vidReader)); % get second frame
  Fr2 = im2double(Fr2);

    % compute Vx, Vy by HS
    [Vx, Vy] = OpticalFlow(Fr1, Fr2, alpha, N);
    m = getMagnitude(Vx, Vy);    

    Fr1 = Fr2; % Fr2 becomes first frame of next sequence
    [rows, cols] = size(m);    
end

magnitude matrix = m

Answer 1

[Walter Roberson]

[vals, index] = sort(m(:), 'descend');
selected_index = index(1:10);
mt = 0 * m;   %same size and type but all 0
mt(selected_index) = m(selected_index);
m = mt;

Note: you need to figure out how you want to handle ties.

[Jae Min Lee]

Thank you very much

[Steven Lord]

mt = 0 * m; %same size and type but all 0

This is true unless m contains a nonfinite value.

I'd prefer calling maxk with two output arguments to generate vals and selected_index, filling all of m with 0, then using those maxk outputs to put the maximum values back in place.

[Walter Roberson]

Good point.