How to speed up this script

Hey,

I am reading data from a text file using the following script:

tic

 for i = 1:2:length(Data);

    Data2(i).H0_SoundSpeed = typecast(uint32(hex2dec(cell2mat(Data{i,1}(1,65:68)))),'single');
    Data2(i).H0_Points = hex2dec(cell2mat(Data{i,1}(1,135:136)));
    Data2(i).R0_SectionName = convertCharsToStrings(char(hex2dec(Data{i,1}(1,137:138))));
    Data2(i).R0_ScalingFactor = typecast(uint32(hex2dec(cell2mat(Data{i,1}(1,141:144)))),'single');     
    Data2(i).A2_SectionName = convertCharsToStrings(char(hex2dec(Data{i,1}(1,657:658))));
    Data2(i).A2_AngleFirst = typecast(uint32(hex2dec(cell2mat(Data{i,1}(1,661:664)))),'single'); 
    Data2(i).A2_ScalingFactor = typecast(uint32(hex2dec(cell2mat(Data{i,1}(1,665:668)))),'single');
    Data2(i).I1_ScalingFactor = typecast(uint32(hex2dec(cell2mat(Data{i,1}(1,1209:1212)))),'single');
    Data2(i).A2_AngleStep(1) = 0 ;
    
     for j = 1 : Data2(i).H0_Points ;
     
     factor = Data2(i).H0_SoundSpeed * Data2(i).R0_ScalingFactor / 2 ;
     Data2(i).R0_Range(j) = factor * hex2dec(cell2mat(Data{i,1}(1, (2*j+143):(2*j+144)))); 
     Data2(i).A2_AngleStepTemp(j) = hex2dec(cell2mat(Data{i,1}(1, (2*j+691):(2*j+692)))); 
     Data2(i).A2_AngleStep(j) = Data2(i).A2_AngleFirst + (sum(Data2(i).A2_AngleStepTemp(1:(j)))*Data2(i).A2_ScalingFactor);
     Data2(i).I1_Intensity(j) = Data2(i).I1_ScalingFactor * hex2dec(cell2mat(Data{i,1}(1, (2*j+1211):(2*j+1212))));
     
     end

end

Data2 = rmfield(Data2, 'A2_AngleStepTemp' );

toc

It is not the most efficient way of reading it in but it works, however it is a bit slow.

I was wondering if anybody has some tips on how I can speed it up.

Thanks!

Answer 1

[Vidhi Agarwal]

Hi @Bram Surewaard,

To improve the performance of your MATLAB script, try considering given optimization:

• Preallocation: Preallocating memory for structures and arrays can significantly enhance performance by reducing the need for MATLAB to dynamically resize data structures during execution.
• Vectorization: Replace loops with vectorized operations where possible.
• If a calculation is repeated within a loop but yields the same result each time, try computing it once before the loop and store it in a variable.

Below is the revised version of the code with above consideration:

tic

% Preallocate the Data2 structure array with the anticipated size
Data2(length(Data)/2) = struct('H0_SoundSpeed', [], 'H0_Points', [], 'R0_SectionName', [], ...
    'R0_ScalingFactor', [], 'A2_SectionName', [], 'A2_AngleFirst', [], ...
    'A2_ScalingFactor', [], 'I1_ScalingFactor', [], 'A2_AngleStep', [], ...
    'R0_Range', [], 'A2_AngleStepTemp', [], 'I1_Intensity', []);

% Iterate over Data with a step of 2
for i = 1:2:length(Data)
    dataRow = Data{i,1}; % Extract the data row once to avoid repeated indexing

    % Extract and convert values
    Data2(i).H0_SoundSpeed = typecast(uint32(hex2dec(dataRow(65:68))), 'single');
    Data2(i).H0_Points = hex2dec(dataRow(135:136));
    Data2(i).R0_SectionName = convertCharsToStrings(char(hex2dec(dataRow(137:138))));
    Data2(i).R0_ScalingFactor = typecast(uint32(hex2dec(dataRow(141:144))), 'single');
    Data2(i).A2_SectionName = convertCharsToStrings(char(hex2dec(dataRow(657:658))));
    Data2(i).A2_AngleFirst = typecast(uint32(hex2dec(dataRow(661:664))), 'single');
    Data2(i).A2_ScalingFactor = typecast(uint32(hex2dec(dataRow(665:668))), 'single');
    Data2(i).I1_ScalingFactor = typecast(uint32(hex2dec(dataRow(1209:1212))), 'single');
    
    % Preallocate arrays for the loop
    numPoints = Data2(i).H0_Points;
    Data2(i).A2_AngleStep = zeros(1, numPoints);
    Data2(i).R0_Range = zeros(1, numPoints);
    Data2(i).A2_AngleStepTemp = zeros(1, numPoints);
    Data2(i).I1_Intensity = zeros(1, numPoints);
    
    factor = Data2(i).H0_SoundSpeed * Data2(i).R0_ScalingFactor / 2;
    angleFirst = Data2(i).A2_AngleFirst;
    angleScale = Data2(i).A2_ScalingFactor;
    intensityScale = Data2(i).I1_ScalingFactor;
    
    % Calculate values in a loop
    for j = 1:numPoints
        rangeIndex = 2*j + 143;
        angleStepIndex = 2*j + 691;
        intensityIndex = 2*j + 1211;
        
        Data2(i).R0_Range(j) = factor * hex2dec(dataRow(rangeIndex:rangeIndex+1));
        Data2(i).A2_AngleStepTemp(j) = hex2dec(dataRow(angleStepIndex:angleStepIndex+1));
        Data2(i).A2_AngleStep(j) = angleFirst + sum(Data2(i).A2_AngleStepTemp(1:j)) * angleScale;
        Data2(i).I1_Intensity(j) = intensityScale * hex2dec(dataRow(intensityIndex:intensityIndex+1));
    end
end

% Remove temporary field
Data2 = rmfield(Data2, 'A2_AngleStepTemp');

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Hope this Helps!