CURVEINTERP is the jOceans module of jLab.

 CURVEINTERP  Interpolate a field or its gradient onto a set of curves.
 
    CURVEINTERP is a low-level function called by CLOSEDCURVES and
    CURVEMOMENTS.
 
    FC=CURVEINTERP(X,Y,F,XC,YC) interpolates the field in matrix F, with 
    axes X and Y, onto the curves specified by XC and YC.  
 
    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.
 
    Unlike INTERP2, CURVEINTERP permits XC and YC to be cell arrays of 
    column vectors, in which case FC will be a cell array of the same size.
    This is useful for working with CLOSEDCURVES and CURVEMOMENTS.
 
    CURVEINTERP uses a fast loopless algorithm that is an order of 
    magnitude faster than looping over the individual curves. 
 
    CURVEINTERP works by calling INTERP2 with the 'linear' algorithm.
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    Gradient interpolation
 
    GRADFC=CURVEINTERP(X,Y,F,XC,YC,'gradient') alternately interpolates not
    F, but instead its *gradient*, and returns the result in the complex-
    valued quantity GRADFC=dF/dX+sqrt(-1)*dF/dY.
   
    This can be very useful when F is large, because it is not necessary
    to compute the gradient of F everywhere.  It is only computed locally
    in near the curves, which can lead to a considerable speed improvment.
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    See also CLOSEDCURVES, CURVEMOMENTS.
 
    'curveinterp --t' runs a test.
 
    Usage: fc=curveinterp(x,y,f,xc,yc);
           gradfc=curveinterp(x,y,f,xc,yc,'gradient');
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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