TRAJWRAP is the jOceans module of jLab.

 TRAJWRAP  Wraps Lagrangian trajectories to fit within a periodic domain.
 
    CX=TRAJWRAP(CX,L) wraps the complex-valued Lagrangian trajectory CX to 
    fit within the doubly periodic domain with edges at +/- L.  
 
    CX specifies the particle position in complex-valued form CX=X+iY.
 
    CX may be of any dimension, but time is assumed to increase along rows.
    The output array will be the same size as the input array.  
 
    Set L=[LX LY] to specify different periodicities in the X and Y 
    directions. Use L=[LX NaN] for only zonal periodicity, or L=[NaN Ly] 
    for only meridional periodicity.
 
    CX=TRAJWRAP(CX,L,'nans') optionally sets the discontinuties resulting
    from wrapping to values of NaN, for plotting purposes.  Note that the 
    output is in this case still the same size as the input. 
 
    [CX1,CX2,...,CXN]=TRAJWRAP(CX1,CX2,...CXN,L) also works for multiple
    arrays of trajectories with the same periodicity.
 
    TRAJWRAP(CX1,CX2,...CXN,L); with no output arguments overwrites the 
    original named input variables.
 
    See also TRAJUNWRAP. 
 
    'trajwrap --t' runs a test.
    'trajwrap --f' generates a sample figure.
 
    Usage: cx=trajwrap(cx,L);
           cx=trajwrap(cx,[Lx Ly],'nan');
           cx=trajwrap(cx,[Lx Ly]);
           [cx1,cx2]=trajwrap(cx1,cx2,[Lx Ly]);
           trajwrap(cx1,cx2,[Lx Ly]);
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    This is part of JLAB --- type 'help jlab' for more information
    (C) 2014--2015 J.M. Lilly --- type 'help jlab_license' for details