Re: Why can't Mathematica tell when something is algebraically
- To: mathgroup at smc.vnet.net
- Subject: [mg108206] Re: Why can't Mathematica tell when something is algebraically
- From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
- Date: Wed, 10 Mar 2010 06:28:38 -0500 (EST)
- References: <201003081109.GAA03756@smc.vnet.net> <2870450.1268136686103.JavaMail.root@n11> <201003100647.BAA03126@smc.vnet.net>
This is, of course, the same bug that has already been explained by Adam Strzebonski: In[1]:= FullSimplify[ r^2 Sqrt[(r^3 + r + 2)/r] - Sqrt[r^3 (r^3 + r + 2)] == 0] Out[1]= True In[1]:= Unprotect[Holonomic`HolonomicFullSimplify]; Clear[Holonomic`HolonomicFullSimplify]; In[3]:= FullSimplify[ r^2*Sqrt[(r^3 + r + 2)/r] - Sqrt[r^3*(r^3 + r + 2)] == 0] Out[3]= Sqrt[r^3*(r^3 + r + 2)] == r^2*Sqrt[(r^3 + r + 2)/r] Andrzej Kozlowski On 10 Mar 2010, at 07:47, David Park wrote: > In view of the counterexamples that seems like a bug. > > > David Park > djmpark at comcast.net > http://home.comcast.net/~djmpark/ > > > From: leigh pascoe [mailto:leigh at evry.inserm.fr] > > > Le 08/03/2010 12:09, mmdanziger a =C3=A9crit : >> 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 >> >> >> > In[2]:= FullSimplify[r^2 Sqrt[(r^3+r+2)/r]-Sqrt[r^3 (r^3+r+2)]==0]= > Out[2]= True > > In[4]:= $Version > Out[4]= 7.0 for Microsoft Windows (32-bit) (February 18, 2009) > > Leigh > > >
- References:
- Why can't Mathematica tell when something is algebraically zero?
- From: mmdanziger <mmdanziger@gmail.com>
- Re: Re: Why can't Mathematica tell when something is algebraically
- From: "David Park" <djmpark@comcast.net>
- Why can't Mathematica tell when something is algebraically zero?