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


Thanks. As with much or most use of LegendreP the argument  mu is real.  My
point and concern is in the Subject:

"LegendreP (Symbolic) is different in Mathematica 5 than previous versions
(M4, M3 ..)"

Your comment means ttht the Mathematica 5 result is not simply 'a different form'  but 
'the wrong
answer'?

Peter


----- Original Message ----- 
From: "Andrzej Kozlowski" <akoz at mimuw.edu.pl>
To: mathgroup at smc.vnet.net
Subject: [mg51490] Re: [mg51413] 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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