Integration of functions over geometries

You can take a quadrangle or a hexahedron and easily map into into a hypercube by a coordinate transformation, at which point you can apply any quadrature rule for a hypercube (with a corresponding Jacobian factor), whether it is a simple first-order bilinear rule or a tensor product of Gaussian quadrature rules or an adaptive quadrature scheme.

More generally, things like triangular domains can also be converted to rectangles with a change of variables, and general polygons could be decomposed into triangles, etcetera.

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