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## Re: sine wave equations

**From**: |
Miroslaw Kwasniak |

**Subject**: |
Re: sine wave equations |

**Date**: |
Sun, 3 Dec 2006 14:52:26 +0100 |

**User-agent**: |
Mutt/1.5.9i |

On Sat, Dec 02, 2006 at 12:45:02PM -0800, Paul Roberts wrote:
>* Most likely just an aliasing problem.*
I'm sure that it is.
>* Make sure that you have a high*
>* enough sampling frequency in x. For example, lets say that x*
>* represents space. The spatial frequency of your sine wave seems to be*
>* 1/lambda. To sample the function properly, your delta_x should be at*
>* least as small as lambda/2. So you would use:*
>* *
>* delta_x = lambda/2;*
>* x = x_min:delta_x:x_max;*
Don't forget that the sampling theorem (known as Nyquist or Shannon theorem,
I suppose that most official name is now: Whittaker-Kotelnikov-Shannon
theorem) is about an uniform-sampled representation of time-continous
signal, which can be perfectly (and uniquely) reconstructed from samples.
If don't like playing with a signal reconstruction/interpolation but only
want to use samples to make a plot I always say - use at least 10 samples
for signal period (that is 5 points for a half sine) to get a sensible figure.
>* If you wanted to oversample, you could use a smaller delta_x*