Unwrap list of angles

[ben]

Dear all

I am looking for a Mathematica-analogue of the unwrap function in another system:
I have a list of angles and want to add multiples of 2*pi to them, so
that there
are no 'jumps' between subsequent entries.
Is there a ready-made function?

Bye
Ben

[luhao]

Hi, Ben
Do you mean confine then in a certain range (as [0, Pi])?

A "dirty" way is:
Table[Random[Real, 100], {i, 1, 100}];
Cos[%];
ArcCos[%]

Hao

[gardyloo]

Hi, Ben,

I ended up writing a version of this a while ago. Here's the
definition I use. The first is for a list of one dimension; it's used in
the second definition (since I usually deal with lists of two dimensions
where the second element in the ordered pairs is the phase.

UnwrapPhase[list_ /; Length[Dimensions[list]] == 1] :=

Module[{newTest,

lC =

Mod[

ListCorrelate[{-1, 1}, list], Pi, -Pi/2]}, newTest[1] = list[[1]];

newTest[i_] := newTest[i] = newTest[i - 1] + lC[[i - 1]];

newTest[#] & /@ Range[Length[list]]]

UnwrapPhase[list:{{_,_}..} ]:=

Transpose[

{

list[[All, 1]],

UnwrapPhase[list[[All,-1]]]

}

]

Hope that helps!

C.O.

ben wrote:
> Dear all
>
> I am looking for a Mathematica-analogue of the unwrap function in another system:
> I have a list of angles and want to add multiples of 2*pi to them, so
> that there
> are no 'jumps' between subsequent entries.
> Is there a ready-made function?
>
> Bye
> Ben
>
>
>
>

--
==========================================================
Curtis Osterhoudt
gard...@mail.remove_this.wsu.and_this.edu
PGP Key ID: 0x088E6D7A
Please avoid sending me Word or PowerPoint attachments
See http://www.gnu.org/philosophy/no-word-attachments.html
==========================================================

[Daniel Lichtblau]

ben wrote:
> Dear all
>
> I am looking for a Mathematica-analogue of the unwrap function in another system:
> I have a list of angles and want to add multiples of 2*pi to them, so
> that there
> are no 'jumps' between subsequent entries.
> Is there a ready-made function?
>
> Bye
> Ben

Here are a couple of MathGroup posts on this topic. As author of the
first one, I'd say go with the second.

http://forums.wolfram.com/mathgroup/archive/1998/May/msg00107.html
http://forums.wolfram.com/mathgroup/archive/1998/May/msg00105.html

Daniel Lichtblau
Wolfram Research

[gardyloo]

Hi, all,

This is in response to a relatively old (about two months' worth)
message concerning unwrapping phases. I realized a while ago that the
algorithm I sent to Ben (and to the list) was wrong -- it *usually*
works, but it does NOT ALWAYS return a phase whose sine matches the
original number fed to it. Therefore, if the original algorithm is used,
it can sometimes return incorrect values.

Here's a more reliable algorithm; I haven't found any problems with
it yet:

(*********** UnwrapPhase follows *************)

UnwrapPhase[data_?VectorQ, tol_:Pi, inc_:2 Pi] :=

FixedPoint[

# +

inc*FoldList[

Plus, 0.,

Sign[

Chop[

ListCorrelate[{1, -1}, #],

tol] (*close Chop*)

] (*close Sign*)

]&, (*close FoldList*)

data] (*close FixedPoint and overall function *)

UnwrapPhase[list:{{_,_}..} ]:=

Transpose[

{

list[[All, 1]],

UnwrapPhase[list[[All,-1]]]

}

]

(*********** UnwrapPhase above *************)

I hope the previous thing I sent hasn't screwed anyone up!

C.O.

gardyloo wrote:
> Hi, Ben,
>
> I ended up writing a version of this a while ago. Here's the
> definition I use. The first is for a list of one dimension; it's used in
> the second definition (since I usually deal with lists of two dimensions
> where the second element in the ordered pairs is the phase.
>
> UnwrapPhase[list_ /; Length[Dimensions[list]] == 1] :=
>
> Module[{newTest,
>
> lC =
>
> Mod[
>
> ListCorrelate[{-1, 1}, list], Pi, -Pi/2]}, newTest[1] = list[[1]];
>
> newTest[i_] := newTest[i] = newTest[i - 1] + lC[[i - 1]];
>
> newTest[#] & /@ Range[Length[list]]]
>
> UnwrapPhase[list:{{_,_}..} ]:=
>
> Transpose[
>
> {
>
> list[[All, 1]],
>
> UnwrapPhase[list[[All,-1]]]
>
> }
>
> ]
>
>
>
>
> Hope that helps!
>
> C.O.
>

> ben wrote:
>
>> Dear all
>>
>> I am looking for a Mathematica-analogue of the unwrap function in another system:
>> I have a list of angles and want to add multiples of 2*pi to them, so
>> that there
>> are no 'jumps' between subsequent entries.
>> Is there a ready-made function?
>>
>> Bye
>> Ben
>>
>>
>>
>>
>>
>
>