       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

>

```

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