John Michell answered . 2024-05-19 02:57:36

The quiver arrows all have fairly small magnitudes which makes it difficult to see the arrows but you can reproduce the figure and zoom in inspect parts of the image.

See inline comments for details.

% Load the data
data = load('average_vels.mat');
% Extract quiver variable for readability
x = data.output_avg(:,1); 
y = data.output_avg(:,2); 
u = data.output_avg(:,3); 
v = data.output_avg(:,4); 
% Compute signed magnitude of the quiver vectors where 
% positive magnitudes point upward and neg mags point downward
z = hypot(u,v) .* sign(v);
% Reshape the z vector into a matrix where 
% zMat(i,j) is the value at x=xVec(i) and y=yVec(j).
[xVec,~, zRow] = unique(x); 
[yVec,~, zCol] = unique(y);
zMat = nan([numel(xVec),numel(yVec)]); 
zIdx = sub2ind(size(zMat),zCol, zRow); 
zMat(zIdx) = z;
% Plot the "heatmap" first
clf()
imagesc(xVec, yVec, zMat)
set(gca, 'YDir', 'Normal') 
cbh = colorbar();
ylabel(cbh, 'Vector magnitude (positive is upward')
axis equal
% add the quiver data
hold on
quiver(x,y,u,v)

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