Re: square waves

[Paul Kienzle]

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



-------------------------------------------------------------
Octave is freely available under the terms of the GNU GPL.

Octave's home on the web:  http://www.octave.org
How to fund new projects:  http://www.octave.org/funding.html
Subscription information:  http://www.octave.org/archive.html
-------------------------------------------------------------