On May 21, 5:35 am, Juanlu001 <juanlu...@gmail.com> wrote: > Yesterday I was playing with symbolic expressions, and I had to apply > divide_both_sides(), and I encountered something funny: you can divide > by zero (with a bit of care). To show this, I've taken the classic > "proof" and created a worksheet: > > http://flask.sagenb.org/home/pub/65/ > > Though I have got useful notices using other functions (such as "Is x > greater than zero?" when trying to solve an equation), I think that an > assumption should be made about the expression we are dividing by to > finally make the division.
Believe it or not, this probably is a feature. Usually when people are using symbolics in Sage, this is the desired behavior - similar to how sage: 3*x-3*x 0 Yes, even for division. This is Ginac, and Maxima does the same thing: (%i3) f: (a-b)*(a+b)=(a-b)*b; (%o3) (a - b) (b + a) = (a - b) b (%i4) f/(a-b); (%o4) b + a = b The questions you get is for when there is really a different answer - integration, solving at times - and those are Maxima messages. Otherwise, every time someone tried to divide, we'd have to ask them interactively whether that was nonzero. That would be a huge burden. At least, I think that is the rationale for why Ginac and Maxima do this. W|A seems to do it too, but I'm not familiar enough with Mma syntax to confirm this conclusively. However, if you don't want this, you could use the hold keyword. sage: f.mul(1/(a-b),hold=True) ((a - b)*(a + b) == (a - b)*b)/(a - b) Or with lhs() etc. Unfortunately, this doesn't seem to be implemented for the divide_both_sides thing, though that's not surprising, since I don't think it's used as much as it could be. - kcrisman -- To post to this group, send an email to sage-devel@googlegroups.com To unsubscribe from this group, send an email to sage-devel+unsubscr...@googlegroups.com For more options, visit this group at http://groups.google.com/group/sage-devel URL: http://www.sagemath.org
