Re: Re: Element test
- To: mathgroup at smc.vnet.net
- Subject: [mg61393] Re: [mg61217] Re: Element test
- From: leigh pascoe <leigh at cephb.fr>
- Date: Tue, 18 Oct 2005 02:44:34 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Jens-Peer Kuska wrote: >Hi, > >what may MemberQ[] do ?? >Element[] is for infinite/uncountable quantities. > >Regards > Jens > >"leigh pascoe" <leigh at cephb.fr> schrieb im >Newsbeitrag news:dii8pd$9cq$1 at smc.vnet.net... >| 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 >| > > > > Thank you Jens and Joerg, I was misled by the usual notation in set theory of epsilon denoting whether x is an element of a set. I am surprised that this does not work for a finite set. However MemberQ does what I want and I am now looking in the correct section of the Help documentation. LP