histogram of angles in a loop

for i=1:n

for j=1:n

angle = transpose(rnorm{i})*rnorm{j};

if angle < cosd(20)

here for every 'i' i want histogram wrt to angles

end

end

end

i need to transform the above code in such a way that for each 'i' histogram(angles) [gap of 0.5 upto 20] has to be stored

rnorm is a 3*1 matrix

urs help is highly appretiated thanks

Answer 1

[Vidhi Agarwal]

Hi @SINDU GOKULAPATI,

To transform your code such that for each i, you calculate the histogram of angles with a specific bin width and store these histograms, you can follow these steps.

• Iterate over each pair (i, j), calculate the angle, and if it meets the condition, store it in a list. After processing all pairs for a given i, we'll compute the histogram and store it.

Sample code for the same is gievn below:

% Sample data
n = 10; 
rnorm = arrayfun(@(x) rand(3, 1), 1:n, 'UniformOutput', false); % Example 3x1 vectors

% Preallocate a cell array to store histograms
histograms = cell(n, 1);

% Define the bin edges for the histogram
binEdges = 0:0.5:20;

% Loop through each 'i'
for i = 1:n
    angles = []; % Initialize an array to store angles for this 'i'
    
    for j = 1:n
        % Calculate the dot product and normalize it
        dotProduct = transpose(rnorm{i}) * rnorm{j};
        normProduct = norm(rnorm{i}) * norm(rnorm{j});
        
        % Ensure the value is within the valid range for acosd
        cosTheta = dotProduct / normProduct;
        cosTheta = min(max(cosTheta, -1), 1); % Clamp the value
        
        % Calculate the angle in degrees
        angle = acosd(cosTheta);
        
        % Check the angle condition
        if angle < 20
            angles(end + 1) = angle; % Append the angle to the list
        end
    end
    
    % Compute and store the histogram for the current 'i'
    histograms{i} = histcounts(angles, binEdges);
end

% Display the histograms for each 'i'
for i = 1:n
    figure;
    histogram('BinEdges', binEdges, 'BinCounts', histograms{i});
    title(['Histogram of Angles for i = ', num2str(i)]);
    xlabel('Angle (degrees)');
    ylabel('Frequency');
end

For better understanding of "histcounts" refer to the documentation: https://www.mathworks.com/help/matlab/ref/double.histcounts.html

Hope that helps!