Unexpectred results using Mod and Unwrap

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I was playing with the Unwrap function when I noticed some unexpected results when working with a phase angle in degrees instead of radians.
The unwarp function unwarps a signal by adding or subtracting a multiple of 2*x. So, in theory unwarp(signal,x) and mod(signal, 2*x) should cancel eachother. This is true for x=pi, but does not seem to hold for any other number. See the example below:
x = pi; % x=pi : ok, x=4 : trouble
% Make some random numbers
signal = 2*x*rand(1,1000);
% Mod(signal,2*x) should be equal to Mod(unwrap(signal,x),2*x)
plot(mod(signal,2*x), mod(unwrap(signal,x),2*x));
Can anybody tell me what I'm missing?

Accepted Answer

Walter Roberson
Walter Roberson on 23 Oct 2012
This caught me off guard a few years ago. The answer is that although you can adjust the jump tolerance, you cannot adjust the amount of the jump.
See http://www.mathworks.com/help/matlab/ref/unwrap.html and think about the implications of the note highlighted there about the effect of specifying a tolerance less than Pi (i.e., that the lower tolerance doesn't change the jump value in that note.)

More Answers (1)

Ruben de Bruin
Ruben de Bruin on 23 Oct 2012
thanks Walter! You just saved my evening :-)

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