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Subject: Re: find zero values of sinc
Date: Fri, 19 Dec 2008 19:25:03 +0000 (UTC)
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"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