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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
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