Dynamically generating a set of combinations for elements of a vector

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Mark Thompson 2016-10-18

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https://ww2.mathworks.cn/matlabcentral/answers/307842-dynamically-generating-a-set-of-combinations-for-elements-of-a-vector

评论： Mark Thompson 2016-10-19

Hi there,

I have to dynamically define a vector m = (m_x, m_y, m_z) where each of the 3 elements in m can take values between -Nm and Nm creating a set of (2Nm +1)^2 combinations. Can anyone help me define all combinations of the possible values of m for a given value of Nm?

Thank you!!

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Answer 1

Walter Roberson 2016-10-18

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https://ww2.mathworks.cn/matlabcentral/answers/307842-dynamically-generating-a-set-of-combinations-for-elements-of-a-vector#answer_239543

http://www.mathworks.com/matlabcentral/answers/304602-out-of-memory-error-using-ndgrid

The functions I show there are for 6 sets, but otherwise the code is generalized -- notice there that the first thing I do is toss the values to select from into a cell array, so you can follow on from after that step if your values are already in a cell array.

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Mark Thompson 2016-10-19

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Hi Walter,

I have managed to look at your method, and whilst technically it appears to be providing a "mesh" of combinations it doesn't present all of the combinations back in groups of 3 values (i.e. mx, my and mz).

I did learn that I have access to the combvec() function with my current MATLAB license so I have managed to implement this solution using the following:

Nm = 6;
mx = (-1*Nm):1:Nm;
my = (-1*Nm):1:Nm;
mz = (-1*Nm):1:Nm;
m = combvec(mx,my,mz)';

The resulting array (2197x3) m after executing this code contains 2197 rows of unique combinations of mx, my and mz, which is what I was originally after.

Thank you again for providing your method for consideration though.

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