Services & Resources / Wolfram Forums / MathGroup Archive
-----

MathGroup Archive 2008

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: need help

  • To: mathgroup at smc.vnet.net
  • Subject: [mg87325] Re: need help
  • From: dh <dh at metrohm.ch>
  • Date: Tue, 8 Apr 2008 05:33:33 -0400 (EDT)
  • References: <ftcoug$ksr$1@smc.vnet.net>


Hi Tomi,

for random numbers, see RandomInteger or RandomReal in the manual. They 

can generates lists.

The function can be written e.g. as:

FourSumf[n_]:=Module[{eq},

eq={x1^2+x2^2+x3^3+x4^2==n,

0<=x1<=x2<=x3<=x4,

Element[{x1,x2,x3,x4},Integers]};

{x1,x2,x3,x4}/.ToRules[Reduce[eq]]

]

here we used that the sum of squares is n, that 0<=xi, we sorted xi 

ascending and we request that x must be integers. Finally Reduce does 

the actual work.

hope this helps, Daniel



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? For example 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 then 2^2+1^2+1^2+1^2

> 

> Is anyone out there have any ideas?

> Thanks All,

> Tomi

> 




  • Prev by Date: Re: need help
  • Next by Date: Re: RegionPlot color
  • Previous by thread: Re: need help
  • Next by thread: Re:need help