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Re: LegendreP (Symbolic) is different in Mathematica5 than previous versions (M4, M3 ..)


On 16 Oct 2004, at 17:20, peteraptaker wrote:

> LegendreP[1,1,mu]
> Out[with m4] = -Sqrt[1 - mu^2]
> Out[with m5] = Sqrt[(-1 - mu)/(-1 + mu)]*(-1 + mu)
>
> While this ( and common sense) show they are equal ..
>
> dum = m4 - m5 // FullSimplify
> PowerExpand[dum]
> Out[]= 0
>

Well, it seems to me that the commonsense thing to do in such 
situations is not to rely too much on common sense and even less on 
PowerExpand. In fact your two expressions are certainly not equal:

a[mu_] := -Sqrt[1 - mu^2];
b[mu_] := Sqrt[(-1 - mu)/(-1 + mu)]*(-1 + mu);

a[2]
(-I)*Sqrt[3]

FullSimplify[b[2]]

I*Sqrt[3]


Andrzej Kozlowski
Chiba, Japan
http://www.akikoz.net/~andrzej/
http://www.mimuw.edu.pl/~akoz/


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