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Re: Possible Bug Report: CoefficientList

  • To: mathgroup at smc.vnet.net
  • Subject: [mg88876] Re: Possible Bug Report: CoefficientList
  • From: dh <dh at metrohm.ch>
  • Date: Tue, 20 May 2008 02:26:09 -0400 (EDT)
  • References: <g0rker$dte$1@smc.vnet.net>


Hi,

consider the variable x in the definition of Chances. This is a global 

variable that can be changed by anybody, what is very dangerous. This is 

exactly what happens in Table[...]. You must localize this variable e.g. 

using Module.

Hope this helps, Daniel



anglewyrm at yahoo.com wrote:

> Here is a function using CoefficientList[] that produces a list:

> Chances[dice_, sides_] := CoefficientList[Expand[(Sum[x^i, {i,

> sides}])^dice], x];

> 

> (* This works: *)

> Chances[3, 6]

> Chances[4,6]

> Chances[5,6]

> 

> (* This fails: *)

> Table[ Chances[x, 6], {x, 3, 5}]

> 

> CoefficientList::ivar: 1 is not a valid variable. >>

> CoefficientList::ivar: 2 is not a valid variable. >>

> CoefficientList::ivar: 3 is not a valid variable. >>

> General::stop: Further output of CoefficientList::ivar will be

> suppressed during this calculation. >>

> 




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