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MathGroup Archive 2000

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bug alert!

  • To: mathgroup at smc.vnet.net
  • Subject: [mg25301] bug alert!
  • From: Jack Goldberg <jackgold at math.lsa.umich.edu>
  • Date: Tue, 19 Sep 2000 03:45:22 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

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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