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Re: PLOT question [message #22971 is a reply to message #22970]

Wed, 20 December 2000 16:01

Craig Markwardt
Messages: 1869
Registered: November 1996

Senior Member

Stuart Colley <src@star.ucl.ac.uk> writes:

> I have some data that is periodic, y=f(t) and the data is plotted as
> plot, t, y The problem is I'd like t to plot phase angle rather than
> time, the problem being the phase angle is between 0 and 1 and repeats.
> Attempting to plot the data you just get a plot between 0 and 1, what I'd
> like to be able to plot is each cycle of the data with it's phase angle.
>
> Any ideas on how to get the plot axes right?

It's not clear to me that everybody else is going waaaayyy overboard
here. Stuart hasn't responded so that may be a good or a bad sign.

Are you just asking how to convert linear time into phase? Perhaps
this is best accomplished with the MOD operator. If your signal has
period P, and the starting epoch is T0, then this may do the trick.

phase = (t-t0)/p MOD 1
phase = (phase+1) MOD 1
plot, phase, y

The "MOD 1" takes the remainder when divided by 1, or simply the
fractional value. The "extra" MOD step there is because MOD doesn't
handle negative numbers very well. It maps the segment from -1 to 0
back onto 0 to 1. Another way to do it in one step is

phase = (t-t0)/p
phase = phase - floor(phase)

Craig

--
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Craig B. Markwardt, Ph.D. EMAIL: craigmnet@cow.physics.wisc.edu
Astrophysics, IDL, Finance, Derivatives | Remove "net" for better response
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[Message index]

		Re: PLOT question By: Martin Schultz on Thu, 21 December 2000 09:44
		Re: PLOT question By: Jaco van Gorkom on Thu, 21 December 2000 06:05
		Re: PLOT question By: Stuart Colley on Thu, 21 December 2000 03:46
		Re: PLOT question By: davidf on Wed, 20 December 2000 16:40
		Re: PLOT question By: Craig Markwardt on Wed, 20 December 2000 16:14
		Re: PLOT question By: Craig Markwardt on Wed, 20 December 2000 16:01
		Re: PLOT question By: Paul van Delst on Wed, 20 December 2000 10:51
		Re: PLOT question By: Dave Greenwood on Wed, 20 December 2000 10:32
		Re: PLOT question By: davidf on Wed, 20 December 2000 10:16

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