Shap2d07.dat, 7th 'shape' file for CPO2D
General conic section, alternative form, defined by users equations.
See also shap2d06.
The difference between this and shap2d06 is that here we generate an ellipse that has its major axis in the r direction, while in shap2d06 that axis is in the z direction.
The form of the general formula that we now use is still
r*r = a*z*z + 2*R*z,
but now a = 1/(e*e - 1), which effectively exchanges the r and z axes for an ellipse.
This form is not suitable for parabolic sections.
In the data above, a = -4, corresponding to e = 0.866, an ellipse.
The range of z is given as 0.01 to 0.5, giving r = 0.14 to 0.0, passing through a maximum value of 0.5 at z = 0.25, and so giving a complete ellipse except for the opening aperture.