Changes in sasmodels/models/rectangular_prism.py [393facf:31df0c9] in sasmodels
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sasmodels/models/rectangular_prism.py
r393facf r31df0c9 12 12 the prism (e.g. setting $b/a = 1$ and $c/a = 1$ and applying polydispersity 13 13 to *a* will generate a distribution of cubes of different sizes). 14 Note also that, contrary to :ref:`parallelepiped`, it does not compute 15 the 2D scattering. 14 16 15 17 … … 24 26 that reference), with $\theta$ corresponding to $\alpha$ in that paper, 25 27 and not to the usual convention used for example in the 26 :ref:`parallelepiped` model. 28 :ref:`parallelepiped` model. As the present model does not compute 29 the 2D scattering, this has no further consequences. 27 30 28 31 In this model the scattering from a massive parallelepiped with an … … 62 65 units) *scale* represents the volume fraction (which is unitless). 63 66 64 For 2d data the orientation of the particle is required, described using 65 angles $\theta$, $\phi$ and $\Psi$ as in the diagrams below, for further details 66 of the calculation and angular dispersions see :ref:`orientation` . 67 The angle $\Psi$ is the rotational angle around the long *C* axis. For example, 68 $\Psi = 0$ when the *B* axis is parallel to the *x*-axis of the detector. 69 70 For 2d, constraints must be applied during fitting to ensure that the inequality 71 $A < B < C$ is not violated, and hence the correct definition of angles is preserved. The calculation will not report an error, 72 but the results may be not correct. 73 74 .. figure:: img/parallelepiped_angle_definition.png 75 76 Definition of the angles for oriented core-shell parallelepipeds. 77 Note that rotation $\theta$, initially in the $xz$ plane, is carried out first, then 78 rotation $\phi$ about the $z$ axis, finally rotation $\Psi$ is now around the axis of the cylinder. 79 The neutron or X-ray beam is along the $z$ axis. 80 81 .. figure:: img/parallelepiped_angle_projection.png 82 83 Examples of the angles for oriented rectangular prisms against the 84 detector plane. 85 67 **The 2D scattering intensity is not computed by this model.** 86 68 87 69 … … 126 108 ["c2a_ratio", "", 1, [0, inf], "volume", 127 109 "Ratio sides c/a"], 128 ["theta", "degrees", 0, [-360, 360], "orientation",129 "c axis to beam angle"],130 ["phi", "degrees", 0, [-360, 360], "orientation",131 "rotation about beam"],132 ["psi", "degrees", 0, [-360, 360], "orientation",133 "rotation about c axis"],134 110 ] 135 111
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