Logical indexing 3D array to get a 2D slice

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Yi-xiao Liu
Yi-xiao Liu 2021-3-12
回答： Walter Roberson 2021-3-12
I have a piece of code that calculates potential for 3D space. Now I want to extract the potential at the YOZ plane:
[X,Y,Z]=meshgrid(-500:spacing:500);
V= some calculations;
V0=V(X==0);
The problem is that V0 is a 1D vector instead of a 2D matrix. How do I correctly extract the slice?

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Walter Roberson
Walter Roberson 2021-3-12
You cannot. When you use a single parameter logical vector to index an array, the result is always a vector.
In limited circumstances you can reshape() the vector.
I suggest something more like
marginals = -500:spacing:500;
[X,Y,Z] = meshgrid(marginals);
V= some calculations;
xtarget = 0;
[~, xidx] = min(abs(marginals - xtarget));
V0 = permute(V(xidx, :, :), [2 3 1]); %safer than squeeze()

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