How to resolve "Transparency violation error" for parallel programming?

I am trying to use parallel programming for the following code, but I am unable to resolve the error which I am facing. Any hint/solution is highely appreciated.

%Data Import and elimination of bad taps from contour plot---------1
tic
index_file_name = linspace(1800,3600,37);
angle = linspace(180,360,37);
data2(:,667:end)=[];


parfor ii = 1:37
    wind_angle = angle(ii);
    Name = ['ADW100o100D040a',num2str(index_file_name(ii)),'.hdf']
    data = hdfread(Name, 'Tap_Coordinates_3D');
    data2 = double(transpose(hdfread(Name, 'Time_Series')));


index = find(data(2,:)==5);
tap5 = [data(:,index);data2(:,index)];
sort5 = sortrows(tap5',[5,4,3])';
clear index
index = find(data(2,:)==6);
tap6 = [data(:,index);data2(:,index)];
sort6 = sortrows(tap6',[5,4,3])';
% Single Matrix of coordinates and Timeseries
if wind_angle<=195
    Timeseries = [sort5 sort6(:, 1:105) sort6(:, 107:end)];
elseif wind_angle>=205 && wind_angle<=280
    Timeseries = [sort5(:, 3:end) sort6(:, 1:105) sort6(:, 107:end)];
elseif wind_angle>=240 && wind_angle<=325
    Timeseries = [sort5(:, 3:end) sort6];
else
    Timeseries = [sort5 sort6];
end
% Timeseries = [sort5 sort6];
x = Timeseries(4,:);
y = Timeseries(3,:);

%Voronoi and Pressure Contour--------------------2
pressure = mean(Timeseries(6:end, :))*0.001/0.657^2;
figure;
[xx, yy] = meshgrid(linspace(min(x), max(x)), linspace(min(y), max(y)));
pressure = griddata(x, y, pressure, xx, yy, 'linear');
contourf(xx, yy, pressure,10,'edgecolor', 'none')
shading interp
hold on
scatter(x, y, 'R','.')
plot ([0 125], [40 40], 'black',  'LineWidth', 0.25)
axis([0 125 0 80])
set(gca, 'Ydir', 'reverse', 'FontName', 'Times New Roman')
ylabel('Building width (ft)', 'FontName', 'Times New Roman', 'FontWeight', 'bold')
xlabel('Building length (ft)', 'FontName', 'Times New Roman', 'FontWeight', 'bold')
title(sprintf('Mean pressure contour at Roof - %d^{o} (kN/ft^2)', angle(ii)), 'fontsize', 12)
colorbar
pbaspect([1.5625 1 1])
hold off

end
toc

The output I am receiving is...

Transparency violation error.
See Workspace Transparency in MATLAB Statements.

[Jan]

Just a note not concerning the problem:

index = find(data(2,:)==5);
tap5  = [data(:,index);data2(:,index)];
clear index

% Faster with logical indexing:
index = (data(2,:)==5);  % No FIND
tap5  = [data(:,index); data2(:,index)];
% clear index  % This is a waste of time here!

This looks strange:

elseif wind_angle>=205 && wind_angle<=280
   ...
elseif wind_angle>=240 && wind_angle<=325   

For wind_anle == 240 to 280 there are two options?!

[Jigar]

Hi Jan,

Thank you for your response towards the optimization, and 240 to 325 is changed to 285 to 325.

[Walter Roberson]

Note that graphics done inside parfor will not be displayed. You can do things such as capture the figure to image file, and I think you might be able to copy graphics objects back to the client.

Answer 1

[Swaraj]

The error message you're getting implies that your code is violating the transparency rule. The “parfor” loop in MATLAB can do this, which can result in multiple workers accessing and changing the same variable at once.

Use the “spmd” block in place of “parfor” to correct this. “SPMD” enables parallel loop execution while guaranteeing that transparency is maintained.

See the below documentation for details.

Execute code in parallel on workers of parallel pool - MATLAB spmd (mathworks.com)

The below documentation might also be helpful.

Ensure Transparency in parfor-Loops or spmd Statements - MATLAB & Simulink (mathworks.com)

[Jigar]

Thank you Swaraj, it is working now.