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MathGroup Archive 2004

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Re: UnitStep

  • To: mathgroup at
  • Subject: [mg52355] Re: [mg52326] UnitStep
  • From: yehuda ben-shimol <benshimo at>
  • Date: Wed, 24 Nov 2004 02:32:27 -0500 (EST)
  • References: <>
  • Sender: owner-wri-mathgroup at

Quotation from the help for UnitStep[]
UnitStep[x] represents the unit step function, equal to 0 for x<0 and 1 
for x\[GreaterEqual]0.
When using the rule p->0 for 1/p UnitStep[1-p] you get 1/0 UnitStep[-1]. 
Mathematica tries to evaluate 1/0  first and this causes the error message
If you try UnitStep[p-1] /p  /.p->0 you will get Indeterminate which 
results from evaluating 0/0.
You may try Limit[1/p UnitStep[p-1],p->0] and get 0 Which gives you the 
Limit but not the Value of UnitStep[p-1]/p
I hope this helps

Blimbaum, Jerry AA R22 wrote:

>Why does the following give me 'indeterminate, infinite expression
>encountered', etc. instead of  zero....
>(1/p) UnitStep[p-1] /.p->0
>I defined a function using the UnitStep because p could  = 0  and I
>thought this would be the way around that problem.......but didnt work
>the way I expected.....
>jerry blimbaum

  • References:
    • UnitStep
      • From: "Blimbaum, Jerry AA R22" <>
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