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## Re: how to express sinc * exp?

 From: Al Goldstein Subject: Re: how to express sinc * exp? Date: Thu, 9 Mar 2000 13:48:15 -0800 (PST)

I hadn't seen the Matlab Primer lately so I wondered. Didn't see any links
in Mathworks but got it from altavista. The address ftp.math.ufl.edu/pub/matlab

On Thu, 9 Mar 2000, Dirk Laurie wrote:

> eric skryf:
> >
> > Dear octave expert:
> >
> >   In matlab toolbox siganl processing:
> > b=0.4*sinc(0.4*(-25:25));
> > [H,w]=freqz(b,1,512,2);
> > plot(w,abs(H));
> >
> > work
> >
> > but if I want to let b be the product of sinc and
> > 2*exp(-i*pi)+exp(-i*3*pi)
> > b=0.4*sinc*(2*exp(-i*pi)+exp(-i*3*pi))(0.4*(-25:25));
> >
> > is not work,
> > I got
> > x undefined near line 24 column 37
> > ..................
> > etc.
> >
> > how to modify it to work?
> >
> Dear Eric:
>
> I and others have seen and sometimes answered quite a few of
> your questions on this list, but sooner or later someone will
> have to say it.  And I'm saying it now:
>
>    RTFM   (Read The Friendly Manual)
>
> Get hold of a Matlab primer on the Internet.
> Several are available by following links from
>    http://www.mathworks.com
> Or buy yourself one of the many books for teaching yourself
> Matlab.   Most of what they say is applicable to Octave too.
> It will be faster than asking questions on octave-help.
>
> In the present case,
>
> b=0.4*sinc*(2*exp(-i*pi)+exp(-i*3*pi))(0.4*(-25:25));
>
> you have made two mistakes:
>
> (a)  sinc is a function which requires one argument.
>      You can therefore write "sinc(0.4*(-25:25))"
>      or "x=(0.4*(-25:25)); sinc(x)"
>      but not just sinc.
>
> (b)  ")(" is never legal syntax.  There must always
>      be an operator.
>
> The way to code what I think you mean, is:
>    x=(0.4*(-25:25));
>    b=0.4*sinc(x).*(2*exp(-i*pi*x)+exp(-i*3*pi*x))
>
> Note ".*" for multiplying vectors term by term.
>
> Dirk Laurie
>
>
>
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