MATLAB Function Reference 
Correct phase angles to produce smoother phase plots
Syntax
Description
Q = unwrap(P)
corrects the radian phase angles in a vector P
by adding multiples of when absolute jumps between consecutive elements of P
are greater than the default jump tolerance of radians. If P
is a matrix, unwrap
operates columnwise. If P
is a multidimensional array, unwrap
operates on the first nonsingleton dimension.
Q = unwrap(P,tol)
uses a jump tolerance tol
instead of the default value, .
Q = unwrap(P,[],dim)
unwraps along dim
using the default tolerance.
Q = unwrap(P,tol,dim)
uses a jump tolerance of tol
.
Examples
Example 1. The following phase data comes from the frequency response of a thirdorder transfer function. The phase curve jumps 3.5873
radians between w = 3.0
and w = 3.5
, from 1.8621
to 1.7252
.
w = [0:.2:3,3.5:1:10]; p = [ 0 1.5728 1.5747 1.5772 1.5790 1.5816 1.5852 1.5877 1.5922 1.5976 1.6044 1.6129 1.6269 1.6512 1.6998 1.8621 1.7252 1.6124 1.5930 1.5916 1.5708 1.5708 1.5708 ]; semilogx(w,p,'b*'), hold
Using unwrap
to correct the phase angle, the resulting jump is 2.6959
, which is less than the default jump tolerance . This figure plots the new curve over the original curve.
Note
If you have the Control System Toolbox, you can create the data for this example with the following code.

Example 2. Array P
features smoothly increasing phase angles except for discontinuities at elements (3,1)
and (1,2)
.
P = [ 0 7.0686 1.5708 2.3562 0.1963 0.9817 1.7671 2.5525 6.6759 1.1781 1.9635 2.7489 0.5890 1.3744 2.1598 2.9452 ]
The function Q = unwrap(P)
eliminates these discontinuities.
Q = 0 7.0686 1.5708 2.3562 0.1963 7.2649 1.7671 2.5525 0.3927 7.4613 1.9635 2.7489 0.5890 7.6576 2.1598 2.9452
See Also
untar  unzip 
© 19942005 The MathWorks, Inc.