Re: FullSimplify and negative radicands

*To*: mathgroup at smc.vnet.net*Subject*: [mg110209] Re: FullSimplify and negative radicands*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>*Date*: Tue, 8 Jun 2010 07:08:19 -0400 (EDT)

It's a bug involving simplification of holonomic functions in Mathematica 7, which has already appeared a couple of times on this forum. You can avoid it by evaluating: Unprotect[Holonomic`HolonomicFullSimplify]; Clear[Holonomic`HolonomicFullSimplify]; Andrzej Kozlowski On 7 Jun 2010, at 21:23, Torsten Schoenfeld wrote: > Why does FullSimplify think this equation is true even though x == -3 is > clearly a counterexample? > > In[1]:== equation == Sqrt[x^2 - 1] ==== Sqrt[x + 1] Sqrt[x - 1] > Out[1]== Sqrt[-1 + x^2] ==== Sqrt[-1 + x] Sqrt[1 + x] > > In[2]:== $Assumptions > Out[2]== True > > In[3]:== equation // FullSimplify > Out[3]== True > > In[4]:== equation /. x -> -3 > Out[4]== False > > (This is with Mathematica 7.0.1.0.) >