# Curious Question?

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### #1 neontiger

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Posted 01 June 2007 - 03:38 PM

Hi guys, I have a trouble. I was trying to perform this problem on the classpad:

```Given:

0<a<=1/4

An =  n^(2n) * (2a)^n
-----------------
(2n)!

...determine whether this sequence in convergent. Determine what happens when a=1/4.
In the case this sequence is non-convergent, demonstrate it by using 2 subsequences whose limits are different to each other.```

Then I typed in (in the ClassPad):

```lim		n^(2n) * (2a)^n
-----------------
n->+inf		 (2n)!```

But the classpad didn't give me any solution to this.The classpad just delayed almost a minute and then it returned the same expression without calculating limit. I think the problem is how does the CP to solve factorial expressions algebraically, that's to say, as everybody of us know, something like:

```n!		n!						   1
------ = ------- => simplify and then -------
(n+1)!	(n+1)n!					  (n+1)```

What do you say about all this?

Another question:
Can I define my own factorial function in the classpad giving the following rules?

0! = 1
1! = 1
n! = n(n-1)!

### #2 The_AFX_Master

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Posted 01 June 2007 - 04:51 PM

Another question:
Can I define my own factorial function in the classpad giving the following rules?

0! = 1
1! = 1
n! = n(n-1)!

I think that you can't do such a decomposition on the classpad directly.. I have years without put my hands on Basic, so i don't know if tricking over it could be useful.

In CPLua you can do the job flawlessly via string manipulation. but my personal advice is, do these simplifications by hand.. the calculator isn't magic

### #3 Gaumerie

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Posted 03 June 2007 - 07:40 PM

You should use the Stirling's approximation :
n! ~ sqrt(2 pi n) (n/e)^n (n->+inf)

### #4 PAP

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Posted 04 June 2007 - 09:28 PM

Can I define my own factorial function in the classpad giving the following rules?
0! = 1
1! = 1
n! = n(n-1)!

You can't in CPBasic, because you need to define a recursive function for this, and CPBasic is not able to support even normal functions (they are limited to one command only). However, CPLua supports recursive functions, so you can do it easily.

### #5 Guest_Guest_*

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Posted 04 June 2007 - 10:44 PM

What about using the piecewise function?

piecewise(n=0,1,piecewise(n=1,1,n!))

### #6 PAP

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Posted 07 June 2007 - 10:59 PM

What about using the piecewise function?
piecewise(n=0,1,piecewise(n=1,1,n!))

Obviously a bad idea. You simply reinvent the wheel, because you define a factorial function which uses the built-in factorial.Totally useless. It is impossible to define a decent factorial function in CPBasic. In fact, it is not even possible to define any decent function in CPBasic (recursive or not). But even if you could, it will be very slow, compared to CPLua.

Strange, some people still use CPBasic...

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