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 > >

**References**:**(x-y) DiracDelta[x-y] does not simplify to 0***From:*Alain Cochard <alain@geophysik.uni-muenchen.de>