Path: news.mathworks.com!not-for-mail From: <HIDDEN> Newsgroups: comp.soft-sys.matlab Subject: Re: Summation and its condition Date: Mon, 16 Feb 2009 11:58:01 +0000 (UTC) Organization: The MathWorks, Inc. Lines: 38 Message-ID: <gnbkc9$poe$1@fred.mathworks.com> References: <gnbahb$4id$1@fred.mathworks.com> <gnbftq$m42$1@fred.mathworks.com> Reply-To: <HIDDEN> NNTP-Posting-Host: webapp-03-blr.mathworks.com Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8bit X-Trace: fred.mathworks.com 1234785481 26382 172.30.248.38 (16 Feb 2009 11:58:01 GMT) X-Complaints-To: news@mathworks.com NNTP-Posting-Date: Mon, 16 Feb 2009 11:58:01 +0000 (UTC) X-Newsreader: MATLAB Central Newsreader 1715507 Xref: news.mathworks.com comp.soft-sys.matlab:518554 "John D'Errico" <woodchips@rochester.rr.com> wrote in message <gnbftq$m42$1@fred.mathworks.com>... > "akihiro mizutani" <aki.mizutani@gmail.com> wrote in message <gnbahb$4id$1@fred.mathworks.com>... > > Hello. > > > > I’ve just started to use matlab. > > And I’m stacked in the problem on summation condition. > > > > Now I’m writing a code to get the result of following summation > > > > Sum[(Aj*Ak-Bj*Bk)(Am*An-Bm*Bn)] > > > > Where An and Bn are arrays respectively and length(An)=length(Bn)=N. > > And the summation should be carried out only for those combinations of indices j, k, m, n that satisfy following conditions; > > > > J+k=m+n, j<k, m<n, j<m. > > > > At this, the indices may take any integer value but from 1 to N only. > > > > Does anyone know how to define such conditions and carry out the summation for all combinations which satisfy the conditions? > > I would be grateful if someone gave me a tip for solving the problem. > > If N is at all large, this will be difficult. It > involves O(N^4) terms in the combinatorial > sum, at least if I did my arithmetic correctly. > > So how large is N? > > John Thank you very much for a kind reply. The number of N is up to 2024. Even if it is difficult to solve the problem with such a big number, N, I would be grateful if you show me your idea! Thanks a lot. Akihiro