Hi. thank you for this.
OK, so it's "promoting" the coefficients to a more general set? Where would a sage newcomer like me find documentation for this? cheers Robin On Mon, Jul 4, 2011 at 3:25 PM, D. S. McNeil <dsm...@gmail.com> wrote: >> My understanding was that 'x' was the indeterminate >> of the ring of polynomials over QQ, i.e. the rationals. So how come >> the polynomial >> has coefficients which are not rational? > > Because the polynomial isn't living where you think it does anymore: > > sage: R.<x> = QQ['x'] > sage: R > Univariate Polynomial Ring in x over Rational Field > sage: parent(x) > Univariate Polynomial Ring in x over Rational Field > sage: > sage: f = (x-sqrt(2))*(x+sqrt(2)) > sage: f > (x - sqrt(2))*(x + sqrt(2)) > sage: parent(f) > Symbolic Ring > sage: R(f) > --------------------------------------------------------------------------- > TypeError Traceback (most recent call last) > [...] > TypeError: unable to convert -sqrt(2) to a rational > sage: R(expand(f)) > x^2 - 2 > > In this case, the introduction of the sqrt terms pushed the expression > out of R and into SR. We can convert back, but only if the expression > is in a form that Sage can recognize as belonging to R. > > > Doug > > -- > To post to this group, send email to sage-support@googlegroups.com > To unsubscribe from this group, send email to > sage-support+unsubscr...@googlegroups.com > For more options, visit this group at > http://groups.google.com/group/sage-support > URL: http://www.sagemath.org > -- Robin Hankin Uncertainty Analyst hankin.ro...@gmail.com -- To post to this group, send email to sage-support@googlegroups.com To unsubscribe from this group, send email to sage-support+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-support URL: http://www.sagemath.org
