Element test

• To: mathgroup at smc.vnet.net
• Subject: [mg61180] Element test
• From: leigh pascoe <leigh at cephb.fr>
• Date: Wed, 12 Oct 2005 01:42:05 -0400 (EDT)
• Sender: owner-wri-mathgroup at wolfram.com

```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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