ECCONV is the jEllipse module of jLab.

 ECCONV  Converts between eccentricity measures.
    Y=ECCONV(X,STR) converts the eccentricity measure X into eccentricity
    measure Y as specified by the string STR. 
    STR is of the form 'in2out' where the names 'in' and 'out' may be
    chosen from the following table.
        STR        Name                    Definition  
       'ecc'       Eccentricity            sgn(b)*sqrt(1-b^2/a^2)
       'ell'       Ellipticity             b/a
       'lin'       Linearity               sgn(b)*(a^2-b^2)/(a^2+b^2)
       'circ'      Circularity             2ab/(a^2+b^2) 
       'nu'        Eccentricity angle      asin(b/sqrt(a^2 + b^2))
       'rot'       Rotary ratio            sgn(b)*(a-abs(b))/(a+abs(b))
    where "a" and "b" are the semi-major and semi-minor axes respective. 
    For example, ECC=ECCONV(L,'lin2ecc') converts the ellipse linearity L
    into eccentricity ECC.  
    All quantities are positive for mathematically positive rotation
    and negative for mathematically negative rotation.  Note the linearity
    is undefined for the case of purely circular rotation a=abs(b);
    For further details, see Lilly and Gascard (2006).
    Cell array input/output
    If ECCONV is given cell array input, it returns cell array output.
    Thus X may be a cell arrays of numerical arrays, and the output Y will
    also be a cell array having an identical size as X.
    Usage:   lin=ecconv(b./a,'ell2lin');
    'ecconv --t' runs a test.
    'ecconv --f' generates a sample figure.
    This is part of JLAB --- type 'help jlab' for more information
    (C) 2005--2015 J.M. Lilly --- type 'help jlab_license' for details        

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