Path: news.mathworks.com!not-for-mail From: <HIDDEN> Newsgroups: comp.soft-sys.matlab Subject: Re: find zero values of sinc Date: Fri, 19 Dec 2008 19:25:03 +0000 (UTC) Organization: The MathWorks, Inc. Lines: 22 Message-ID: <gigsef$dhn$1@fred.mathworks.com> References: <gieh8q$1g6$1@fred.mathworks.com> <gignmi$87u$1@fred.mathworks.com> Reply-To: <HIDDEN> NNTP-Posting-Host: webapp-05-blr.mathworks.com Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8bit X-Trace: fred.mathworks.com 1229714703 13879 172.30.248.35 (19 Dec 2008 19:25:03 GMT) X-Complaints-To: news@mathworks.com NNTP-Posting-Date: Fri, 19 Dec 2008 19:25:03 +0000 (UTC) X-Newsreader: MATLAB Central Newsreader 1645635 Xref: news.mathworks.com comp.soft-sys.matlab:508039 "Jonathan " <sievers.notreally.@cita.utoronto.ca> wrote in message <gignmi$87u$1@fred.mathworks.com>... > "David " <REMOVEdavidg@UPPERCASEphy.LETTERSucsf.edu> wrote in message <gieh8q$1g6$1@fred.mathworks.com>... > > hi all: > > > > i want to find the zero values of sinc, where sinc = sin(pi*x)./(pi*x) > > > > x = -5.5:0.1:5.5; > > sinc = sin(pi*x)./(pi*x); > > plot(x, sinc) > > > > > > you can clearly see the zero crossings, but find(sinc == 0) is null (i think) because i've discretized a continuous function, and none of the values are exactly zero. > > > > then i tried to convert sinc into a continuous function: mysinc = @(x)sin(pi*x)./(pi*x) > > (don't ask me why i didn't type mysinc = 'sin(pi*x)./(pi*x)'; instead, because i learn by example) > > > > this is where i get stuck. matlab seems to have good ways to find the roots of polynomials, but this function is not a polynomial. do i need to convert it into a polynomial form using euler relations or something ? > > > > The zeroes are just all integers except for 0. yes! i noticed that, i'm still muddling over that result. i wasn't sure if i should act spooked, or like a dully unimpressed high-school geometry student. the ratio of two irrational numbers giving me the sequence of integers like that. was going to ask about it on mathnerds