How to determine which points in an array are with a ring? Stupid question.

Question

Tim Fulcher 2022-3-2

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评论： Tim Fulcher 2022-3-2

Hi All,

I have an arrays of equal length consisting of x position, y position and energy. I wish to determine which of those entries fall within a ring without resorting to doing it iteratively.

Code (which doesn't work) is:

distances = sqrt(X_Position.^2 + Y_Position.^2);

if (distances > Inner_Radius) & (distances < Outer_Radius)

X_Position_on_Instrument = X_Position;

Y_Position_on_Instrument = Y_Position;

Energy_on_Instrument = Energy;

end

In other words the new arrays (on_Instrument) will only contain values which fall within the ring. I know the answer will be really simple but I can't see it at the mo'.

Thanks again.

Regards

Tim

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Answer 1

Cris LaPierre 2022-3-2

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https://ww2.mathworks.cn/matlabcentral/answers/1662070-how-to-determine-which-points-in-an-array-are-with-a-ring-stupid-question#answer_908055

在 MATLAB Online 中打开

Use logical indexing.

distances = sqrt(X_Position.^2 + Y_Position.^2);
% create logical index to indicate points that meet condition
ind = distances>Inner_Radius & distances<Outer_Radius;
% Use that index to extract the corresponding data
X_Position_on_Instrument = X_Position(ind);
Y_Position_on_Instrument = Y_Position(ind);
Energy_on_Instrument = Energy(ind);