[Maxima] Comparison of compound objects
robert.dodier at gmail.com
Thu Dec 28 12:44:24 CST 2006
On 12/27/06, Stavros Macrakis <macrakis at alum.mit.edu> wrote:
> Currently, Maxima cannot compare strings or lists using is(x<y):
> is( "a"<"b" ) => unable to evaluate predicate
> is(  <  ) => unable to evaluate predicate
> is(  < [1,.2] ) => arguments with incompatible structure
> (even an error with prederror:false )
> I think it would be useful to extend "<" to these cases in the natural
> way, using lexicographic ordering for lists/vectors.
Some people might expect < to map over lists.
If is(a < b) is OK for lists, what about matrices or other objects?
Defining is(a < b) for lists seems inconsistent with the treatment of
other expressions -- is(list(...) < list(...)) would be OK but not
is(foo(...) < foo(...)) for some random operator foo, and when foo is
an arithmetic operator, is(foo(...) < foo(...)) would be defined, but
not consistent with lexicographic ordering for lists.
I guess I'm not comfortable with extending is(a < b) to lists.
But certainly is(a < b) can be usefully defined as orderlessp(a, b)
when a and b are strings.
> 1) Vector norm might be a more natural mathematical comparison.
Well, vector norm only establishes equivalence classes,
and I don't like the general conflation of vectors and lists anyway.
> 2) It might cause some programming errors to not be caught.
That doesn't bother me.
Thanks for thinking about this problem,
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