dummy index list

*To*: mathgroup at smc.vnet.net*Subject*: [mg20256] dummy index list*From*: "Arturas Acus" <acus at itpa.lt>*Date*: Sun, 10 Oct 1999 00:04:08 -0400*Sender*: owner-wri-mathgroup at wolfram.com

Dear Group, I have 2 questions: 1) I want the fastest way to select dummy symbols from some expression. Suppose we have a list of dummy indices {a,-b,c, -d}. What is the fastest way to get rid of the minus sign? Here is my solution: testlist={a,-b,c, -d}; Map[Cases[Flatten[#,Infinity,Times],_Symbol]&,testlist] However I am not satisfied and believe there should be a simple solution for such a simple task. I will use this function very often in future, so it should be as fast as possible. 2) I am not a professional programmer, so I am very interesting in algorithm speed estimates (there was a lot of such estimates published recently in this group). Do some tutorials on the web exist on this subject? At the moment I am interesting in Mathematica SameQ algorithm asymptotic (theoretic). Is it n or log(n) or some other? How one can know or guess this? Probably there are some tables for various basic operations, for example, like 1.the best selection algorithm can be done at speed ?? 2. the list intersection algorithm is ?? 3 the union can be done at ?? and so on. Thanks. Dr. Arturas Acus Institute of Theoretical Physics and Astronomy Gostauto 12, 2600,Vilnius Lithuania E-mail: acus at itpa.lt Fax: 370-2-225361 Tel: 370-2-612906