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MathGroup Archive 2000

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Re: bug alert!

  • To: mathgroup at
  • Subject: [mg25325] Re: [mg25301] bug alert!
  • From: Jack Goldberg <jackgold at>
  • Date: Sat, 23 Sep 2000 03:35:49 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

Well, something is seriously wrong with my so-called "correct"
answer.  It should be  (Floor[x]+1)UnitStep[x].
Sorry :>)


On Tue, 19 Sep 2000, Jack Goldberg wrote:

> Hi group:
> Brief report of a bug: ver 4.0x on  PowerMac and Unix systems.
> Sum[ UnitStep[x-k],{k,0,Infinity} ] -> (1+x)*UnitStep[x]
> which is incorrect.  The correct answer is  Floor[x]*UnitStep[x].
> This error is compounded when you 
> Sum[f[x-k]*UnitStep[x-k],{k,0,Infinity}], 
> in that not only to you get an incorrect answer, the answer contains hidden
> variables and is total nonsense.
> Something is seriously at fault here. 

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