|All smtbx exceptions are derived from this class. More...|
|Special class for "Index out of range." exceptions. More...|
|Refinement namespace. |
Weighting schemes for L.S. (least_squares.h).
Constraints handled as reparametrisation.
Small Molecule Toolbox namespace.
Constraints are in the first place restrictions placed on quantities depending on the refined crystallographic parameters. For example, a tetrahedral C-CH3 is modelled by stating that bond lengths and bond angles, which are functions of the sites of the Hydrogen atoms and of the Carbon they are bonded to, shall keep some fixed values.
Traditionally, those constraints are solved analytically by expressing some of the parameters involved in the constraints as functions of the others, and sometimes of extra parameter, which are usually referred to as "free variables" following the ShelX nomenclature. In the above example, the Hydrogen sites are a function of the Carbon site and of one rotation angle around the C-C bond.
The former presentation is what is known as constraints in numerical optimisation, whereas the latter is how that word is understood in crystallography.