On Fri, Oct 23, 2015 at 5:04 AM, Nathann Cohen <nathann.co...@gmail.com> wrote: > Hello everybody, > > When calling .row() on an immutable matrix, one gets mutable vectors. > I can easily avoid it for the code I am writing, but do you think we > should do something about it?
m.row() returns a new (copy) of the row of the matrix, so making that immutable would be inconsistent with how copy works for matrices. sage: m = matrix.ones(10) sage: m.set_immutable() sage: copy(m).is_immutable() False The set_immutable method on matrices solves exactly *one* problem, which is it makes it possible to create matrices and then efficiently cache them without having to worry about some other code breaking them. For example, it would be very bad indeed if the matrix T below were mutable (like it was for a few years of Sage...): sage: M = ModularSymbols(11) sage: T2 = M.hecke_matrix(2); T2 sage: T2.is_immutable() True There are a **TON** of interesting programming problems that the idea of "immutable data structures" can solve. Designing and implementing immutable data structure that actually solve these problems is interesting and highly nontrivial. It's not done in Sage to much extent. A good example in the Javascript world of a systematic library for immutable data structures, which really solves some interesting problems is https://facebook.github.io/immutable-js/ It provides immutable versions of all standard Javascript data structures, but very efficiently builds them on top of mutable data structures, minimizing wasted space. It would be interesting to have something similar in Sage, at least for matrices/vectors, but don't think that we do now. What's in Sage is really trivial by comparison. For starters, we might create a new immutable vector type in Sage that is a reference to a row in an immutable matrix, etc., etc. It's a lot of work to design and implement something like this. At least you can do "v = m.row(0); v.set_immutable()". -- William > > sage: m = matrix.ones(10) > sage: m.set_immutable() > sage: hash(m.row(0)) > ... > TypeError: mutable vectors are unhashable > > Nathann > > -- > 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. -- William (http://wstein.org) -- 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.
