[PATCH] Use the inf-norm rather than 2-norm in issymmetric; add ishermitian.

[John W. Eaton]

On  7-Dec-2007, Rolf Fabian wrote:

| I strongly argue against most of those changes.
| 
| First of all, backward compatibility is an important issue.
| After the current change of 'issymmetric'
| complex hermitian matrices are not any more considered
| to be 'symmetric' as before and many existing programs
| fail or return weird results.

OK, I agree we should not make that change.  But what about using the
inf-norm instead of the 2-norm?  Is there any harm in that?

| Adding 'ishermitian.m' isn't a good idea either, because
| there exist many more properties of square matrices
| with respect to their internal symmetry which
| are not yet implemented into Octave. 

| [...]

| So I suggest to keep the 'issymmetric.m' function
| for backward compatibility, remove the 'ishermitian.m'
| again  and add a single new function which takes a particular
| symmetry pattern as an argument like e.g. 
| 
| retval = symmetry( x, mode, tol )
| 
| where retval is true, if square matrix x pocesses symmetry pattern mode =
| 'symmetric', 'skewsymmetric', 'hermitian', 'skewhermitian',
| 'centrosymmetric', ... 'persymmetric', ... 'bisymmetric', ... (24 patterns)
| Of course the mode patterns should be also available as short acronyms.
| 
| Actually this function exists already since several years as part of my
| personal linear algebra Octave toolkit. If interested I'll send it to you.

Sure, post it here.

jwe