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Re: a couple of gripes

  • To: mathgroup at
  • Subject: [mg29765] Re: [mg29751] a couple of gripes
  • From: BobHanlon at
  • Date: Sun, 8 Jul 2001 01:00:09 -0400 (EDT)
  • Sender: owner-wri-mathgroup at

In a message dated 2001/7/7 2:37:22 AM, J.A.Solomon at writes:

>When I evaluate 
>I don't get 
>When I evaluate 
>I don't get 


"4.1 for Power Macintosh (November 2, 2000)"

If[x == y, 1, 0] is equivalent to DiracDelta[x - y]

Integrate[f[x]*DiracDelta[x-y], {x, -Infinity, Infinity}]



The PDF of the normal distribution evaluated at the mean is

PDF[NormalDistribution[mu, sigma], mu]


As the standard deviation, sigma, approaches zero, the PDF evaluated at the 
will become arbitrarily large, not 1.  Presumably, you are trying to evaluate 
CDF at the mean+ as the standard deviation approaches zero.  

CDF[NormalDistribution[mu, 10^(-n)], mu+10^(1-n)]

(1/2)*(1 + Erf[5*Sqrt[2]])



For arbitrarily large n this is the case with the standard deviation 
arbitrarily small 
and the CDF evaluated arbitrarily close to the mean.

Bob Hanlon
Chantilly, VA  USA

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