cross check different implementations of the same shape

[pkienzle]

There are many instances where the same shape can be described with two different models. For example,

• core-shell models vs. core-only models with the sld of the shell matching the sld of the core and the radius of the core+shell matching the radius of the core,

• sphere:ellipsoid with r_major and r_minor equal to r,

• barbell:pearl_necklace with 2 pearls

• barbell:sphere with hemispherical bell and length 0 bar

• rectangular_prism:parallelepiped, one using ratios the other using lengths

• etc.

Collect a list of these in sasmodels and check that the values correspond.

Furthermore, for oriented models, the 1-D model should match the orientation average of the 2-D model.

[pkienzle]

The sphere equivalent of barbell and capped cylinder show that they are inaccurate at high qr values, with a jump at 0.04 with radius 5000. To see this, use:

sascomp -midq -double -nq=1000 sphere,barbell radius=5000 radius_bell=radius length=0