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MathGroup Archive 2001

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Re: a couple of gripes

  • To: mathgroup at smc.vnet.net
  • Subject: [mg29773] Re: a couple of gripes
  • From: "Allan Hayes" <hay at haystack.demon.co.uk>
  • Date: Sun, 8 Jul 2001 01:00:17 -0400 (EDT)
  • References: <9i6aan$okh$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Joshua,

Re the first example: we do have

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

        f[y]

Re the second example:  problems are likely if the formal variable  x is
also used for the mean.
A normal distribution with zero standard deviation zero seems also to be
related to DiracDelta function.


Allan
---------------------
Allan Hayes
Mathematica Training and Consulting
Leicester UK
www.haystack.demon.co.uk
hay at haystack.demon.co.uk
Voice: +44 (0)116 271 4198
Fax: +44 (0)870 164 0565

"Joshua A. Solomon" <J.A.Solomon at city.ac.uk> wrote in message
news:9i6aan$okh$1 at smc.vnet.net...
> When I evaluate
> Integrate[f[x]*If[x==y,1,0],{x,-Infinity,Infinity}]
> I don't get
> f[y].
>
> When I evaluate
> PDF[NormalDistribution[x,0],x]
> I don't get
> 1.
>
> js
> --
> Joshua A. Solomon
> Department of Optometry and Visual Science
> City University
> London EC1V 0HB
> Voice: (44) 20 7040 0192
> Secretary/Fax: (44) 20 7040 0182
> J.A.Solomon at city.ac.uk
> http://www.staff.city.ac.uk/~solomon
>
>




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