Re: unwrap modulo 2pi

[Dave Greenwood <greenwoodde(at)ornl.gov>]

I wrote:
> graham_wilson@my-deja.com wrote:
> > My appologies for not being explicit enough...
> >  
> > IDL> a=[2,4,6,8,10,12]
> > IDL> a=[2.,4.,6.,8.,10.,12.]
> > IDL> b=2*!PI
> > IDL> c=a mod b
> > IDL> print, c
> >       2.00000  4.00000   6.00000   1.71681  3.71681   5.71681
> >  
> > What I mean by 'unwraping' is: Given I know 'c' and 'b' how do I
> > explicitly find a?
>  
> Surely I must be missing something(?):
>  
>  IDL> print, c + fix(a/b)*b
>       2.00000      4.00000      6.00000      8.00000      10.0000      12.0000

And a proverbial ohnosecond later I went - "Oh No!".  I guess I better
go back to lurking.  ;-(

Btw, given that (a mod b) = (a+(n*b) mod b) do you expect your 'unwraping'
function to give the lowest value of a such that c = a mod b?

Dave