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Re: Re: Unexpected non-evaluation problem
*To*: mathgroup at smc.vnet.net
*Subject*: [mg63157] Re: [mg63142] Re: Unexpected non-evaluation problem
*From*: Andrzej Kozlowski <akoz at mimuw.edu.pl>
*Date*: Fri, 16 Dec 2005 07:22:10 -0500 (EST)
*References*: <dnrch3$kie$1@smc.vnet.net> <200512151107.GAA24729@smc.vnet.net>
*Sender*: owner-wri-mathgroup at wolfram.com
On 15 Dec 2005, at 20:07, Jean-Marc Gulliet wrote:
> Carl Cotner wrote:
>> I am totally baffled by the following Mathematica behavior:
>>
>> In[1]:= InverseFourierTransform[FourierTransform[x^2, x, y], y, x]
>> Out[1]= Sqrt[2 Pi] x^2 FourierTransform[DiracDelta[y], y, x]
>>
>> In[2]:= Sqrt[2 Pi] x^2 FourierTransform[DiracDelta[y], y, x]
>> Out[2]= x^2
>>
>> I've already asked my local guru without success, so I'm hoping
>> someone
>> here can help me. Does anyone know why the first expression doesn't
>> evaluate to x^2 all by itself? How I can force it to do so?
>>
>> Carl
>>
> Hi Carl,
>
> Mapping *Evaluate* to all parts will do it. Why? I do not know...
>
> In[1]:=
> Evaluate //@ InverseFourierTransform[FourierTransform[x^2, x, y],
> y, x]
>
> Out[1]=
> x^2
>
> Best regards,
> /J.M.
>
Another possible workaround is to wrap Unevaluated around the
argument of InverseFourierTransform:
In[1]:=
InverseFourierTransform[Unevaluated[FourierTransform[x^2,
x, y]], y, x]
Out[1]=
x^2
Essentially the same approach is:
InverseFourierTransform[FourierTransform[u, x, y], y,
x] /. u -> x^2
x^2
There is no mystery why this works: both approaches are based on the
obvious fact:
InverseFourierTransform[FourierTransform[u, x, y], y,
x]
u
It seems hard to tell what causes the original problem, except that
it is certainly a bug.
Andrzej Kozlowski
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