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MathGroup Archive 2005

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

  • To: mathgroup at smc.vnet.net
  • Subject: [mg56296] Re: (x-y) DiracDelta[x-y] does not simplify to 0
  • From: Alain Cochard <alain at geophysik.uni-muenchen.de>
  • Date: Thu, 21 Apr 2005 05:36:15 -0400 (EDT)
  • References: <d42kg5$39t$1@smc.vnet.net> <d45agf$ieu$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Dr. Wolfgang Hintze writes:
 > Alain,
 > 
 > may I add the strangest case I found up to now:
 > 
 > case wh01
 > In[3]:=Simplify[(x - y)*DiracDelta[x - y], {x, y}]
 > Out[3]=0
 > 
 > But also these are strange enough
 > 
 > case wh02
 > In[7]:=Simplify[(x - y)*DiracDelta[x - y], {x && y}]
 > Out[7]=0
 > 
 > case wh03
 > In[13]:=Simplify[(x - y)*DiracDelta[x - y], {x || y}]
 > Out[13]=(x - y)*DiracDelta[x - y]
 > 
 > case wh04
 > In[29]:=Simplify[I*x*DiracDelta[I*x]]
 > Out[29]=0
 > 
 > But
 > case wh05
 > In[30]:=Simplify[I*DiracDelta[I]]
 > Out[30]=I*DiracDelta[I]
 > 
 > Can't explain ...
 > Wolfgang

I have not much experience with delta functions with complex numbers,
so I don't have an opinion on wh04 and wh05, but I indeed find
wh01->03 funny.  Hope some will tell us what's going on.

Alain



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