How can I calculate max and min in degree?

I've got an Array with my Phase Phi in degrees:[ 170°,179°,180°,-179°...] ranging from -180° to 180° and I want to calculate how much it drifts over time. My current method of

   phi = [ 170,179,180,-179]
   drift =max(phi)-min(phi)

doesn't work, because 180°-(-179°) = 359°, while it should be 11°(from 170° to -179°). The Problem is that degrees are a cylic(x°= (x-360)°) unit unlike most units.

Is the a smart way to calculate the maximum phase drift?

[Image Analyst]

If it goes from 179 to -179, isn't that a difference of 2? From 179 to 180 is 1, and 180 is the same as -180, so then from -180 to -179 is another 1, for a total of 2. At least that's how I view it.

[Matthias]

It was a little confusing. I tried to fix that. Now you can enter the Example in Matlab

Answer 1

[Mischa Kim]

How about

 drift = max(abs(diff(phi)));

By the way, how do you get 11°? Is that from a different set of data points not shown in your vector above?

[Matthias]

170° and -179° are 11° appart. I want the maximum overall drift. Diff would only give me neighbouring drifts.

If I had a non-cyclic unit like e.g. Volts this would simply be done by:

Vdrift = max(V) - min(V)

[Mischa Kim]

Understood. Do you have access to the Statistics Toolbox?

 phi   = [170,179,180,-179]';
 drift = max(pdist(phi + 360*(phi<0)));

[Matthias]

This seems to just shift the problem:

     phi = [4,-4]';drift = max(pdist(phi + 360*(phi<0)))

drift =

     352

Answer 2

[Walter Roberson]

Use unwrap() before the diff()