Re: Question on defining a digital signal x[n]

[Juan Pablo Carbajal]

On Wed, May 8, 2013 at 9:38 PM, Oceanic <address@hidden> wrote:
> Hello,
>
> Some background - I am currently teaching myself DSP and have recently taken
> a Signals & Systems course.
> As part of the process I am also learning how to use Octave.
>
> As a learning exercise I am going back to see if I can use Octave instead of
> pen-and-paper to go through past examples and exercises. I will probably be
> asking a lot of questions and hopefully I can can get some help. I would
> like to make a preemptive apology for the noob questions
>
> So first question:
>
> I have a digital signal described as follows:
> x[n] = 0, when n <= -3 and when n >= 2
> x[n] = 1, otherwise
>
> I described the signal successfully (at least a window of the signal, since
> it extends to +ve and -ve infinity) using the following code (contents of .m
> file below):
>
> y = ones(1,20);
> x = [-10:9];
> n = length(x);
> for i = 1:n
>   if x(i) <= -3 | x(i) >= 2
>     y(i) = 0;
>   end
> end
>
> stem(x,y)
> axis([-15 15 -1 1.5])
>
> My question is - Is there a more efficient way to describe this signal
> (probably without having to use a for-loop)? What are the best-practices for
> describing such signals?
>
> Thank you.
>
>
>
>
> --
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You can do it without a for loop.  What you do is create vectors of
boolean variables... example below
(signal that is 1 if input is between -n and n)

function y = signal (t,n)
  tf = t >= -n & t <= n;
  y = zeros(size(t));
  y(tf) = 1;
endfunction

You can generalize this. Also check in the signal package in
Octave-forge[1] exmaples like sigmoid_train [2]

[1] http://octave.sourceforge.net/signal/overview.html
[2] http://octave.sourceforge.net/signal/function/sigmoid_train.html