[bug #68238] linsolve: 2nd output should return rcond for square matrix, rank for nonsquare

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Update of bug #68238 (group octave):

         Planned Release:                    None => 12.1.0 (current default)

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Follow-up Comment #1:

Documentation changes are free and can be made on stable.  Can you prepare a
changeset in the next 2 weeks for that issue?  We still have time before 11.2
bug fix release.

I think the m-file solution is fine proposed is fine for the development
branch.  First, the second output is optional and probably most of the time
isn't calculated.  Second, there is additional computation in not harvesting R
directly from the output of LAPACK routines in C++.  But, it hardly matters
compared to the programmer time required to implement it.  See benchmarking
below.


A = rand (100);
tic; rc = rcond (A); toc
Elapsed time is 0.000286102 seconds.

A2 = rand (100,101);
tic; rnk = rank (A2); toc
Elapsed time is 0.000976801 seconds.


The calculation of rank is not even taking 1 millisecond.



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