Unwrap with tolerance other than default (=pi)

I encountered a problem with the Matlab function “unwrap” when I tried to unwrap the phase of a signal with a jump tolerance other than pi. I used the following phase for testing the behavior of the “unwrap” function:

phs  = [0.1, 0.2, 0.3, 0.4, 0.4+pi-0.1, 0.4+pi-0.05, 0.4+pi-0.01];

There is a jump in the phase angle between elements four and five that is smaller than pi. I then tried to eliminate this jump using the “unwrap” function and the tolerance pi/2:

phs = unwrap(phs,  pi/2);

The phs vector didn’t change. It also didn’t change by using any other value for the tolerance. Shouldn’t it eliminate the jump by adding +/- 2pi or by adding +/- pi/2?

[Siegfried Martius]

perhaps this can help

phs_un=unwrap(2*phs)/2

[Bryan Wingert]

I know I'm resurrecting a dead thread, but this aspect of the unwrap function frustrated me. See this answer for an explanation of why this hack works, and how to adapt it.

https://www.mathworks.com/matlabcentral/answers/2005722-unwrap-lower-than-the-default-value-pi

Answer 1

[David Goodmanson]

Hello pSchi, from 'doc unwrap':

Note A jump tolerance less than π has the same effect as a tolerance of π. For a tolerance less than π, if a jump is greater than the tolerance but less than π, adding ±2π would result in a jump larger than the existing one, so unwrap chooses the current point. If you want to eliminate jumps that are less than π, try using a finer grid in the domain.