Mathematica 9 is now available
Services & Resources / Wolfram Forums
-----
 /
MathGroup Archive
2005
*January
*February
*March
*April
*May
*June
*July
*August
*September
*October
*November
*December
*Archive Index
*Ask about this page
*Print this page
*Give us feedback
*Sign up for the Wolfram Insider

MathGroup Archive 2005

[Date Index] [Thread Index] [Author Index]

Search the Archive

Re: (x-y) DiracDelta[x-y] does not simplify to 0

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56225] Re: [mg56198] (x-y) DiracDelta[x-y] does not simplify to 0
  • From: yehuda ben-shimol <bsyehuda at gmail.com>
  • Date: Wed, 20 Apr 2005 05:29:55 -0400 (EDT)
  • References: <200504190854.EAA02509@smc.vnet.net>
  • Reply-to: yehuda ben-shimol <bsyehuda at gmail.com>
  • Sender: owner-wri-mathgroup at wolfram.com

As I remember, DiracDelta is singular and has a meaning only under integration.
Anyway the properties of the DiracDelta are kept by Mathematica
i.e.,
Integrate[(x - y)DiracDelta[x - y], {x, -1, 1}, {y, -1, 1}]
returns 0 as expected
yehuda

On 4/19/05, Alain Cochard <alain at geophysik.uni-muenchen.de> wrote:
> Mathematica 4.0 for Linux
> Copyright 1988-1999 Wolfram Research, Inc.
>  -- Motif graphics initialized --
> 
> Considering that
> 
>      In[1]:= FullSimplify[x DiracDelta[x]]
> 
>      Out[1]= 0
> 
> I was surprised about this one:
> 
>      In[2]:= FullSimplify[(x-y) DiracDelta[x-y]]
> 
>      Out[2]= (x - y) DiracDelta[x - y]
> 
> whereas:
> 
>      In[3]:= FullSimplify[(x-y) DiracDelta[x-y]/.x-y->z]
> 
>      Out[3]= 0
> 
> Is it simply that Mathematica is a little weak on Out[2], or does it have a
> good reason for not simplifying, i.e., am I missing something at the
> mathematics level?
> 
> Thanks in advance,
> Alain
> 
>


  • Prev by Date: Re: holding boxes verbatim
  • Next by Date: Re: Integrating a complicated expression involving Sign[...] etc.
  • Previous by thread: (x-y) DiracDelta[x-y] does not simplify to 0
  • Next by thread: Re: (x-y) DiracDelta[x-y] does not simplify to 0