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MathGroup Archive 2005

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Re: Element test

  • To: mathgroup at smc.vnet.net
  • Subject: [mg61218] Re: Element test
  • From: Joerg Schaber <schaber at molgen.mpg.de>
  • Date: Thu, 13 Oct 2005 01:39:28 -0400 (EDT)
  • References: <dii8pd$9cq$1@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Hi,

to test wether an element is member of a list you might try
In[61]:=
(#\[Equal]39)&/@{4,2,9,39,40}

Out[61]=
{False,False,False,True,False}

best,

joerg

leigh pascoe wrote:
> Dear Group,
> 
> I have a defined a graph that is a function of n, gr1[n], with n^2 +4 
> vertices and 2n(n+1) edges.
> 
> I would like to remove some edges from this graph, corresponding to all 
> edges leading to the vertices in the set list[n]. Since Ma doesn't seem 
> to have a PERL like Foreach construct, I tried something like the following:
> 
> In[42]:=
> Do[If[Element[i,list[6]],
>     ShowGraph[test=DeleteEdges[gr1[6],{{{i,j}} ,{ j,1,40}}],
>       VertexNumber\[Rule]True]],{i,1,40}]
> 
> Unfortunately this doesn't work. The problem (apart from possible syntax 
> errors) seems to lie in the fact that
> 
> Element[i, list[6]] never evaluates to True. For a specific example 
> using the list {4,2,9,39,40},
> 
> In[33]:=
> Element[39,list[6]]
> Out[33]=
> 39\[Element]{4,2,9,39,40}
> 
> whereas the similar statement
> 
> In[27]:=
> 149\[Element]Primes
> Out[27]=
> True
> 
> How can I delete the edges to the vertices in list[n] from my graph?
> 
> Thanks
> 
> LP
> 


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