Re: Why can't Mathematica tell when something is
- To: mathgroup at smc.vnet.net
- Subject: [mg108144] Re: [mg108074] Why can't Mathematica tell when something is
- From: DrMajorBob <btreat1 at austin.rr.com>
- Date: Tue, 9 Mar 2010 06:22:40 -0500 (EST)
- References: <201003081109.GAA03756@smc.vnet.net>
- Reply-to: drmajorbob at yahoo.com
Your expression is NOT identically zero, since, for instance: r^2 Sqrt[(r^3 + r + 2)/r] - Sqrt[r^3 (r^3 + r + 2)] /. r -> I -2 + 2 I When r is Real, on the other hand: r^2 Sqrt[(r^3 + r + 2)/r] - Sqrt[r^3 (r^3 + r + 2)] // PowerExpand 0 Bobby On Mon, 08 Mar 2010 05:09:56 -0600, mmdanziger <mmdanziger at gmail.com> 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. For some reason Simplify or even > FullSimplify can't figure this out. Once you get dependent on > Mathematica these things are pretty disturbing...you forget about your > own knowledge because the program tells you that things are > different. Then you sit there like an idiot checking an algebraic > identity that any beginning precalc student should be able to solve no > problem. > > Is there any way to get Mathematica to "wake up" to these things? It > has such a powerful algebraic engine for most things, why can't it see > something simple like the above? Do you really have to manually > override and tell the program when things should be zero? > > For the time being I'll just sift through and test things by hand but > I can't believe that there isn't a better way. > > Best, > md > -- DrMajorBob at yahoo.com
- References:
- Why can't Mathematica tell when something is algebraically zero?
- From: mmdanziger <mmdanziger@gmail.com>
- Why can't Mathematica tell when something is algebraically zero?