[Octave-bug-tracker] [bug #42422] ismatrix: Matlab is only true for 2 dimensions

[Rik]

Follow-up Comment #9, bug #42422 (project octave):

It is pretty clear that Matlab only uses ismatrix() for checking array
dimensions while Octave also tests that the argument is a "numeric" class
which includes numeric, logical, and character arrays.

A trivial implementation of ismatrix to match Matlab is


retval = (ndims (x) == 2);


But, as I expected, a lot of Octave core code is relying on also checking the
class of the argument.  Substituting the new ismatrix and running 'make check'
results in 47 new test failures.

The closest existing function is isreal() which returns true for numeric,
logical, and character matrices.  It would mean tracking down each of the 47
test failures and verifying that isreal could be substituted there. 
Alternatively, we could create a new function, some
is_close_enough_to_numeric_for_government_work() which includes numeric,
logical, and char types, and replace calls with that new function.

As for performance, I'll file a separate issue report about promoting some of
the frequently used predicate tests into C++ functions.  There is already a
patch report about doing that for isscalar but it should probably be
generalized to include all of the frequently used input validation tests.


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