Re: Why can't Mathematica tell when something is algebraically zero?
- To: mathgroup at smc.vnet.net
- Subject: [mg108155] Re: Why can't Mathematica tell when something is algebraically zero?
- From: Richard Fateman <fateman at cs.berkeley.edu>
- Date: Tue, 9 Mar 2010 06:24:41 -0500 (EST)
- References: <hn2ltj$3kt$1@smc.vnet.net>
mmdanziger wrote:
> This isn't the first time that I've encountered something like this in
> Mathematica but in my calculations I got a term like this:
>
> r^2 Sqrt[(r^3 + r + 2)/r] - Sqrt[r^3 (r^3 + r + 2)]
>
> Which is obviously identically zero.
let f[r_]:= r^2 Sqrt[(r^3 + r + 2)/r] - Sqrt[r^3 (r^3 + r + 2)]
try
Plot[Re[f[x I]], {x, -1, 1}]
from which one can conclude that f[r] is not identically zero when r is
not real.
> For some reason Simplify or even
> FullSimplify can't figure this out.
I'm not sure what to suggest regarding the rest of your message. :)