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Re: ReplaceAll bug
*To*: mathgroup at yoda.physics.unc.edu
*Subject*: Re: ReplaceAll bug
*From*: Silvio Levy <levy at math.berkeley.edu>
*Date*: Fri, 31 Jan 92 20:06:34 PST
> Sqrt[240] /. Sqrt[x_] -> 2 Sqrt[x/4]
> 4 Sqrt[15]
>
> Sqrt[480] /. Sqrt[x_] -> 2 Sqrt[x/4]
> Sqrt[480]
This isn't a problem with ReplaceAll, but with the seemingly random
normalization adopted by Sqrt. Sqrt[240] is automatically converted
to 4 Sqrt[15], then the substitution rule transforms that into
8 Sqrt[15/4], which is automatically normalized again to 4 Sqrt[15]
(try it). In the bottom example, the substitution rule acts first,
giving 2 Sqrt[120], and this is normalized to Sqrt[480]. Does anybody
know if there is any rhyme or reason to these normal forms?
Silvio
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