From help-request at octave dot org Mon Apr 10 20:17:40 2006
Subject: Re: square waves
From: Paul Kienzle <pkienzle at users dot sourceforge dot net>
To: NZG <ngustavson at emacinc dot com>
Cc: Octave Help <help at octave dot org>, Doug Stewart <dastew@sympatico.ca>
Date: Mon, 10 Apr 2006 21:15:51 -0400

On Apr 10, 2006, at 11:39 AM, NZG wrote:
>> See also the function square just added to octave-forge.
> Same thing Matlab has, nice for compatibility but I don't like it 
> because you
> don't get what you expect when you plot it, interpolation gives you a
> trianglish wave instead of a square.
> I think it really needs to use more points to more closely approx. a 
> true
> square.

What is wrong with the following?

   axis([-0.1 1.1 -1.1 1.1])
   t=[0:0.001:1];

   # A 7 Hz square wave sampled at 1kHz with a .25 duty cycle
   plot(t,square(2*pi*t*7,0.25))

   # A 7 Hz sine wave
   plot(t,sin(2*pi*t*7))

If you are using really coarse sampling then you are probably better
off using a stem plot:

   t=[0:0.01:1];stem(t,square(2*pi*t*7,0.25))

Stairs is misleading because of the aliasing.

   t=[0:0.01:1];stairs(t,square(2*pi*t*7,0.25))

If you just want to plot the edges, then you can use e.g.,

   f=7;duty=0.25;
   t=[[0:1/f:1];[0:1/f:1]+duty/f](:);
   stairs(t,(-1).^[0:length(t)-1])

- Paul



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