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MathGroup Archive 2008

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Re: Easiest Mathematica algorhitm needed


On 13 Oct 2008, at 19:20, Artur wrote:

> Dear Mathematica Gurus,
> Who know which Matrhematica function uses to separate square free part
> of number.
> e.g.
> In[1]: Table[Sqrt[n!], {n, 1, 10}]
> Out[1]: {1, Sqrt[2], Sqrt[6], 2 Sqrt[6], 2 Sqrt[30], 12 Sqrt[5], 12
> Sqrt[35],
> 24 Sqrt[70], 72 Sqrt[70], 720 Sqrt[7]}
> What to do to take squre-free parts:
> {1, 2, 6, 6, 30, 5, 35, 70, 70, 7}
> or square parts
> {1, 1, 1, 2, 2, 12, 12, 24, 72, 720}
> Best wishes
> Artur
>


It is a bit surprising that Sqrt does this since there is no  
polynomial time algorithm for factoring the square free part of an  
integer. In fact, we can implement the SquareFreePart algorithm using  
FactorInteger as follows:

SquareFreePart[n_Integer?Positive] := Times @@ Power @@@ ({#[[1]],  
Mod[#[[2]], 2]}& /@ FactorInteger[n])
and
SquarePart[n_Integer?Positive] := n/SquareFreePart[n]

  SquareFreePart /@ Table[n!, {n, 1, 10}]
{1, 2, 6, 6, 30, 5, 35, 70, 70, 7}
  SquarePart /@ Table[n!, {n, 1, 10}]
  {1, 1, 1, 4, 4, 144, 144, 576, 5184, 518400}

I don't think there is any much more efficient way of doing this.

Andrzej Kozlowski






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