Re: What variables are in a function and displaying surds

*To*: mathgroup at smc.vnet.net*Subject*: [mg31127] Re: What variables are in a function and displaying surds*From*: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>*Date*: Fri, 12 Oct 2001 03:36:44 -0400 (EDT)*Organization*: Universitaet Leipzig*References*: <9q2l3v$p4f$1@smc.vnet.net>*Sender*: owner-wri-mathgroup at wolfram.com

Hi, > Is there a way in Mathematica to generate a list of variables in an > expression like Variable[]. For example if I passed the expression > Sin[x+y]+ z/p - t the list {x,y,z,p,t} would be generated. hmm... what may Cases[Sin[x + y] + z/p - t, _Symbol, Infinity] do ? > > Another unrelated question is when I use Mathematica V4.0 to calculate > tables of ThreeJSymbols the outputs Generally consist of fractions of > roots of the form > > Sqrt[a/b] , c/Sqrt[d] and Sometimes Sqrt[e/f]/g > > is there a way to force Mathematica always output them in the form > Sqrt[h]/i > > eg instead of it giving Sqrt[2/3] giving Sqrt[6]/3 No, since Sqrt[6]/3 is automatical simplifyed to Sqrt[2/3] Just look what Trace[Sqrt[2/3] /. Sqrt[a_] :> Sqrt[Numerator[a]*Denominator[a]]/Denominator[a]] does. The only way to prevent this is to make a new Sqrt[] function, i.e. mySqrt[] and In[]:=Sqrt[2/3] /. Sqrt[a_] :> mySqrt[Numerator[a]*Denominator[a]]/Denominator[a] Out[]=mySqrt[6]/3 Regards Jens