Re: Re: Unwrap list of angles

*To*: mathgroup at smc.vnet.net*Subject*: [mg74557] Re: [mg73291] Re: [mg73262] Unwrap list of angles*From*: gardyloo <gardyloo at mail.wsu.edu>*Date*: Mon, 26 Mar 2007 02:04:47 -0500 (EST)*References*: <200702090718.CAA18382@smc.vnet.net> <200702100439.XAA07871@smc.vnet.net>

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 >> >> >> >> >> > > -- ========================================================== Curtis Osterhoudt gardyloo at 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 ==========================================================