On Sat, May 31, 2008 at 5:21 AM, Henryk Trappmann <[EMAIL PROTECTED]> wrote: > > Hello, > > while the general rule of coercing in binary operations seems to be > towards the most unprecise, > for example > RealField(100)(1)*2 == RealField(100)(2) or > RealField(100)(1)*RealField(50)(1) == RealField(50)(1)
The general rule is not "toward the most unprecise". It's more subtle than that. At a bare minimum there is never a canonical (automatic) coercion from elements of R to elements of S unless that coercion is defined (as a homomorphism) on all of R. > this rule seems to be broken when working with log(2) > not RR(1)*log(2) == RR(log(2)) > > Then I read about the coercing rules and found that > RR.__call__(log(2)) is possible but > RR._coerce_(log(2)) raises a type error > > is there reason to do so? As Michel pointed out, log(2) is an element of the symbolic ring. There is no natural homomorphism from the symbolic ring to RR. However, there is a natural homomorphism from RR to the symbolic ring. sage: parent(log(2)) Symbolic Ring sage: parent(x) Symbolic Ring sage: SR._coerce_(RR(3)) 3.00000000000000 sage: RR._coerce_(log(2)) TypeError You can always force coercion using RR(log(2)), as you know. -- William > > > > -- William Stein Associate Professor of Mathematics University of Washington http://wstein.org --~--~---------~--~----~------------~-------~--~----~ 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 -~----------~----~----~----~------~----~------~--~---
