Often in mineral physics, solutions are subject to a set of linear constraints. For example, the set of valid site-occupancies in solution models are constrained by positivity and fixed sum constraints (the amount of each chemical species must be greater than or equal to zero, the sites in the structure are present in fixed ratios). Similarly, the phase amounts in a composite must be more than or equal to zero, and the compositions of each phase must sum to the bulk composition of the composite.
Geometrically, linear equality and inequality constraints can be visualised as a polytope (an n-dimensional) polyhedron. There are several situations where it is convenient to be able to interrogate such objects to understand the space of validity. In BurnMan, we make use of the module pycddlib to create polytope objects. We also provide a number of tools for common chemically-relevant operations.
burnman.MaterialPolytope
burnman.tools.polytope