CLOSEDCURVES is the jOceans module of jLab.

 CLOSEDCURVES  Locate and interpolate closed curves in a possibly periodic domain.
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    [XC,YC]=CLOSEDCURVES(F,FO) returns closed curves of the matrix F at 
    level FO, i.e. curves where F=FO, as the cell arrays XC and YC.  
 
    If F has N contiguous patches at the contour level FO, then XC and YC
    will be length N cell arrays.  
 
    After rounding, the values of XC will be indices into the *columns* 
    of F, while YC will be indices into the *rows*. 
 
    [XC,YC]=CLOSEDCURVES(X,Y,F,FO) alternately specifies X and Y axes to go
    with F.  X is associated with the *columns* of F and Y with its *rows*.
    The lengths of X and Y must match SIZE(F,2) and SIZE(F,1) respectively.
 
    Use CELLPLOT(XC,YC) to plot the curves. 
 
    CLOSEDCURVES works by calling Matlab's CONTOUR routine, re-arranging
    the contour matrix output, and throwing away non-closed contours. 
 
    CLOSEDCURVES has options for considering a periodic domain, and for
    interpolating the curves at a specified resolution, as described below.
 
    The above figure shows closed curves of the Okubo-Weiss parameter P,
    specifically the contour level P = -4 times its own standard deviation,
    in a numerical simulation of quasi-geostrophic (QG) turbulence.
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    Periodic extension
   
    CLOSEDCURVES can look for curves within a singly or doubly periodic
    version of the input field F.
 
    CLOSEDCURVES(...,'periodic') will make F doubly periodic before looking
    for closed curves.  
 
    The X and Y axes will be extended based on their regular spacing, and 
    these extended values will be returned in XC and YC for curves that 
    fall into the periodically extended domain. 
 
    CLOSEDCURVES(...,'periodic',N) extends F by N points in all directions.
 
    CLOSEDCURVES(...,'periodic',N,M) extends F by M points at both the left
    and the right (rows), and N points at the top and the bottom (columns).
 
    To apply the periodic extension in only one of the dimesions, use
    CLOSEDCURVES(...,'periodic',N,0) or CLOSEDCURVES(...,'periodic',0,M).
 
    The above figure illustrates the difference between the periodized and
    non-periodized algorithm.  In periodic domain such as this one, closed
    curves at the region boundary will be missed wihtout periodization.
 
    See PERIODIZE for details.
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    Interpolation
 
    CLOSEDCURVES can also interpolate the curves to a specified number of
    points along each curve, in order to increase the spatial resolution.  
 
    [XC,YC]=CLOSEDCURVES(...,'interpolate',NPOINTS) will spline-interpolate
    each curve to be length NPOINTS. 
 
    In this case, XC and YC will be *matrices* instead of cell arrays.  The
    number of rows of XC and YC is then NPOINTS, with each column 
    corresponding to a separate curve.
 
    Choosing a high value of NPOINTS, say NPOINTS=256, will minimize errors
    in integral calculations based on these curves, such as those carried
    out by CURVEMOMENTS.
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    See also CURVEMOMENTS, CURVEINTERP, PERIODIZE.  
 
    'closedcurves --t' runs a test.
    'closedcurves --f' generates the above figure.
 
    Usage: [xc,yc]=closedcurves(f,fo);
           [xc,yc]=closedcurves(x,y,f,fo);
           [xc,yc]=closedcurves(x,y,f,fo,'interpolate',256);
           [xc,yc]=closedcurves(x,y,f,fo,'periodic',M);
           [xc,yc]=closedcurves(x,y,f,fo,'periodic',N,M);
           [xc,yc]=closedcurves(x,y,f,fo,'periodic',N,M,'interpolate',256);
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    This is part of JLAB --- type 'help jlab' for more information
    (C) 2013--2015 J.M. Lilly --- type 'help jlab_license' for details

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