Hi,
When implementing some algebra element class, I faced the following issue:
the class inherits from sage.structure.element.CommutativeAlgebraElement
and I've implemented the __eq__() and __ne__() methods, but not __cmp__()
because my algebra is not an ordered set. Everything works well (the test
suite for commutative algebras is passed by the parent), but if I construct
matrices from algebra elements f1,...,f4, via
a = matrix([[f1,f2], [f3,f4]])
and compare them by a == b, the following error appears:
NotImplementedError: BUG: sort algorithm for elements of 'algebra of scalar
fields on the 2-dimensional manifold 'M'' not implemented
This is triggered by the lack of method __cmp__() in the algebra element
class. Adding such method via
def __cmp__(self, other):
if self.__eq__(other):
return 0
else:
return -1
fixes the problem.
Hence the question: shall __cmp__() be always implemented in element
classes, even if the parent is not an ordered set ? If yes, what shall it
return when the two elements differ ? -1 as above ? Shall __eq__() be
implemented as well ?
I've noticed that in line 919 of file src/sage/structure/element.pyx, it is
written;
# For a *Python* class just define __cmp__ as always.
I've also noticed that in the example provided in the tutorial How to
implement new algebraic structures in Sage
<http://sagemath.org/doc/thematic_tutorials/coercion_and_categories.html>,
only __cmp__() is implemented, not __eq__().
On the other side, __cmp__() has been withdrawn in Python 3 and only the
rich comparison methods, like __eq__(), remain.
Thanks for your advice on this.
Eric.
--
You received this message because you are subscribed to the Google Groups
"sage-devel" group.
To unsubscribe from this group and stop receiving emails from it, send an email
to sage-devel+unsubscr...@googlegroups.com.
To post to this group, send email to sage-devel@googlegroups.com.
Visit this group at http://groups.google.com/group/sage-devel.
For more options, visit https://groups.google.com/d/optout.
