On 28 February 2018 at 13:49, Ralf Stephan <gtrw...@gmail.com> wrote:
> Why should I define x when Sage gives me a polynomial with x, doesn't it > already know it? > > That's what a user would ask and, frankly, s/he would be right. > Here is one reason. In this example: sage: M=Matrix([[1,2,3],[4,5,6],[7,8,9]]) sage: p = M.charpoly() sage: p.parent() Univariate Polynomial Ring in x over Integer Ring sage: p x^3 - 15*x^2 - 18*x sage: x.parent() Symbolic Ring when we see the polynomial displayed we see the variable displayed as x, but there has been no assignment to the python variable 'x' behind the scenes. You are suggesting (it seems) that after computing p here the python variable 'x' should be bound to p.parent().gen(). But it is surely a very Bad Idea for a function to (re)-assign global variables? This would be a source of many bugs. It would probably be less confusing if there was no globally defined 'x' at all as has been suggested earlier in this thread. Then the last line of my example would raise an error, and the documentation could tell users to enter something like 'x = p.parent().gen()' or 'x = p.variables()[0]' (the latter would be better if a method variable() existed for univariate polynomials!). John > -- > You received this message because you are subscribed to the Google Groups > "sage-support" group. > To unsubscribe from this group and stop receiving emails from it, send an > email to sage-support+unsubscr...@googlegroups.com. > To post to this group, send email to sage-support@googlegroups.com. > Visit this group at https://groups.google.com/group/sage-support. > For more options, visit https://groups.google.com/d/optout. > -- You received this message because you are subscribed to the Google Groups "sage-support" group. To unsubscribe from this group and stop receiving emails from it, send an email to sage-support+unsubscr...@googlegroups.com. To post to this group, send email to sage-support@googlegroups.com. Visit this group at https://groups.google.com/group/sage-support. For more options, visit https://groups.google.com/d/optout.
