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Re: ZTarnsform[Sin[4 n],n,z] OK, but ZTransform[Sin[5 n],n,z,] hangs?

• To: mathgroup at smc.vnet.net
• Subject: [mg56805] Re: ZTarnsform[Sin[4 n],n,z] OK, but ZTransform[Sin[5 n],n,z,] hangs?
• From: Peter Pein <petsie at dordos.net>
• Date: Fri, 6 May 2005 03:00:37 -0400 (EDT)
• References: <d5cth5$mbe$1@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

steve wrote:
> Hello;
> This is Mathematica 5.1 on windows.
> 
> This is a strange one.
> 
> When I start Mathematica and type
> 
> ZTarnsform[Sin[4 n],n,z]
> 
> Then I get the answer.
> 
> but if replace '4' by '5' above, I see Mathematica starts
> to consume huge amount of memory untill the PC hangs running
> out of virtual RAM.
> 
> ZTarnsform[Sin[5 n],n,z]   <---- hangs
> ZTarnsform[Sin[4 n],n,z]   <---- ok
> 
> any one has any idea what is going on? is this some subtle
> mathemtical thing I am overlooking that is causing this?
> what is so special about '5' here? 
> 
> thanks,
> Steve
> 
Hi Steve,

I don't know, what happens in the kernel, but

ZTransform[Sin[a n], n, z] /. a -> 5

gives a quick answer.


-- 
Peter Pein
Berlin