From the discussion in sage-support (which I mistook for sage-devel).
On 02/09/2008, at 6:22, Robert Dodier <[EMAIL PROTECTED]> wrote: > * sets and matrices not distinguished from lists Mathematica's attributes are something I will miss in Sage. (They are a partial fix for some of the problems with a lack of a good "Set") If I instruct mathematica: SetAttributes[set, Orderless] Now create s = set[a,c, b]. It is automatically reordered to s == set[a, b, c]. Because of the attribute "Orderless", nice things like set[a, c, b] == set[c, b, a] are automatically true. There are a number of other useful "Attributes". For example: Let "f" be some undefined function. f[1] remains unevaluated. "N" is the "to_float" function, so that e.g. N[2] -> 2.0. So N[f[1]] becomes f[1.0]. However, if I give f the attribute "NHoldAll", N does not descend into f, so N[f[1]] is f[1]. This is useful for defining things like quantum operators, where you might want to convert an expression's coefficient into a floating point number, without converting any spin quantum numbers inside that expression to inexact quantities. Attributes are not unlike the __ __ members in python. I think there might be a case for a few well-defined mathematical __ __ members appearing widely in sage---the obvious ones are related to the counterparts of mathematica's N and Hold. It might already be the case. D ================================== David J Philp Postdoctoral Fellow National Centre for Epidemiology and Population Health Building 62, cnr Mills Rd & Eggleston Rd The Australian National University Canberra ACT 0200 Australia T: +61 2 6125 8260 F: +61 2 6125 0740 M: 0423 535 397 W: http://nceph.anu.edu.au/ CRICOS Provider #00120C --~--~---------~--~----~------------~-------~--~----~ 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://www.sagemath.org -~----------~----~----~----~------~----~------~--~---
