Eccentricity of ellipse from third flattening
ecc = n2ecc(n) computes the eccentricity of an ellipse (or ellipsoid of revolution) given the parameter n (the "third flattening"). n is defined as (a-b)/(a+b), where a is the semimajor axis and b is the semiminor axis. Except when the input has 2 columns (or is a row vector), each element is assumed to be a third flattening and the output ecc has the same size as n.
ecc = n2ecc(n), where n has two columns (or is a row vector), assumes that the second column is a third flattening, and a column vector is returned.