Robert Bradshaw wrote: > The sage coercion model guarantees that when x.__add__(y) is called > (well, technically x._add_ or x._add_c_impl), the argument y is of > the same type and parent as x. For example > > sage: R.<x> = ZZ[] > sage: x+1/2 > x + 1/2 > sage: parent(x) > Univariate Polynomial Ring in x over Integer Ring > sage: parent(1/2) > Rational Field > sage: parent(x+1/2) > Univariate Polynomial Ring in x over Rational Field > > In your case, someone could type > > sage: g = CompleteGraph(5) > sage: g+1 # will call g.__add__(1) > ??? > > which you have to deal with. Typically, just throw an error if it's > not a graph. But what about graph + digraph? Digraph + digraph? Etc. > Should graph + x be a new graph with a new (unconnected) vertex 'x'?
Thanks for the explanation of the coercion model. That is a very nice way to do things. As for graphs, there isn't a standard definition for the "+" operation that is agreed upon, even for graphs of the same type (e.g., should it be disjoint union or union?). That's why I was asking about custom infix operators, so I could make a disjoint_union infix operator, which was clearly different than the union operator, which was clearly different than whatever else. Another reason for custom infix operators was to allow for all sorts of different kinds of products (just look at the Graph class to see many examples), any of which could be represented as "graph * graph". The best I've come up with at this point is, given graphs A,B,C,D,E, the union is: A.union(B).union(C).union(D).union(E) where the union function returns the modified graph each time so I can keep chaining union function calls. The union actually modifies the graph A, so if you want A left alone and a new graph returned, you do: newgraph=A.copy().union(B).union(C).union(D).union(E) Comments? Is there a better way to do things? With time, I suppose the graph theory community will settle on a commonly accepted meaning for "graph + graph", but as far as I understand, that hasn't happened yet. Thanks, -Jason --~--~---------~--~----~------------~-------~--~----~ To post to this group, send email to sage-devel@googlegroups.com To unsubscribe from this group, send email to [EMAIL PROTECTED] For more options, visit this group at http://groups.google.com/group/sage-devel URLs: http://sage.scipy.org/sage/ and http://modular.math.washington.edu/sage/ -~----------~----~----~----~------~----~------~--~---
