Standard Deviation for 3D data sets

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% USAGE: stadev=ra_std(var)
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% DESCRIPTION: Function computes standard deviation specifically for 3D
% data sets i.e time, lat, lon or lv, lat, lon. to generate spatial plots
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% INPUTS:
% var = variable whose stadev required, must be 3D
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% OUTPUT:
% sd = standard deviation of the variable which will give spatial data output i.e 2D
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% DISCLAIMER:
% Albeit this function is designed only for academic purpose, it can be implemented in
% research. Nonetheless, author does not guarantee the accuracy.
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% ACKNOWLEDGMENT:
% Author is eternally grateful to MathWorks for providing in-built functions.
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