if we use the instruction [~, idx]=sort(abs(A(:))), what is this ~ (NOT) sign represents

Can we replace ~ with any other name

[Stephen23]

The use of the tilde is explained in the documentation, and discussed in the MATLAB blogs:

http://www.mathworks.com/help/matlab/matlab_prog/symbol-reference.html

http://blogs.mathworks.com/loren/2009/09/11/matlab-release-2009b-best-new-feature-or/

http://www.mathworks.com/help/matlab/matlab_prog/ignore-function-inputs.html

Ambitious students should learn how to search for information themselves: they will find that their favorite internet search engine is a good place to start.

Answer 1

[Azzi Abdelmalek]

[e, idx]=sort([2 1 5 8 6])

will return

e= [1 2 5 6 8]
idx=[2 1 3 5 4]

[~, idx]=sort([2 1 5 8 6]

will return just idx. In this case, ~ is not considered as "not" operator

Answer 2

[Jan]

For backward compatibiliy I do not use the tilde ~, but a variable called "dummy".

[Stephen23]

Do you use a pre-R2009b version?

[Jan]

Beside 2015b I'm still using R6.5 and R2009a. While avoiding the tilde is trivial, catch exception required an ugly workaround for R6.5: catch ME_, ME = ME_. And under the historical Matlab a folder is included in the path, which defines the funktion ME_:

function Exception = ME_
persistent LastException
if nargout == 0
   LastException       = lasterror();
   LastException.cause = {};
end
Exception = LastException;

I've backported the standard algebraic methods for single's, typecast, cast, uigetfiles, ancestor, commandwindow, javacomponent, javaObjectEDT.

The reason to maintain such an old system like R6.5 is an extremely well tested large code (>300'000 lines + comments) for clinical decision making and the need to guarantee the reproducibility of the results for 10 years. Fortunately the retirement of WindowsXP allows to skip R6.5 now :-) Bye bye, my beloved dinosaur.

Let me mention that R6.5 runs much faster in a VM with XP than 2015b on the real processor.