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Re: pure function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87363] Re: [mg87332] pure function
  • From: Andrzej Kozlowski <akoz at mimuw.edu.pl>
  • Date: Tue, 8 Apr 2008 07:17:00 -0400 (EDT)
  • References: <200804080934.FAA11916@smc.vnet.net>

On 8 Apr 2008, at 18:34, haitomi wrote:
> Hello All,
>
> I need help with two pure functions
>
> 1)  Li[Ranlist,x] that return a list of x element selected at random  
> from Ranlist.  (Is there any way to gennerate random from Ranlist? I  
> have RanList=Range[-100,100])
>
> 2) the function 4Sumf[x] is computing the sum of 4 squares of x. If  
> I have x=1, this function will gennerate 1^2+0^2+0^2+0^2, if x=4  
> then 2^2+0^2+0^2+0^2, if x=7 2^2+1^2+1^2+1^2
>
> Is anyone out there have any idea?
> Thanks All,
> Tomi
>

With Mathematica 6:

1) Selections with replacement or without replacement?

With replacement:

RandomChoice[Range[-100, 100], 6]
{58, 13, -51, 66, -40, -69}

without replacement:

RandomSample[Range[-100, 100], 6]
{-38, 67, 83, 79, 3, -3}

(2).

PowersRepresentations[1, 4, 2]
{{0, 0, 0, 1}}

PowersRepresentations[7, 4, 2]
{{1, 1, 1, 2}}

All this has to be (and can be) done quite differently with earlier  
versions of Mathematica but as you do not specify your version I  
assume you have the latest.


Andrzej Kozlowski


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