Coefficient extraction
Functions in this module allow easy extraction of monomial coefficients from
many_body_operator_generic objects. Each of extract_*() functions selects
a particular class of monimials (quadratic/quartic) and returns a dictionary,
which maps tuples of monomial indices to the values of the corresponding
coefficients.
Utility function dict_to_matrix() converts such dictionaries into a matrix/tensor representation (interaction U-matrix, for instance) given a valid fundamental operator set.
C++
In order to make code cleaner, the following shorthand types are defined in triqs/operators/util/extractors.hpp,
// Shorthand for many_body_operator_generic
template<typename scalar_t>
using op_t = operators::many_body_operator_generic<scalar_t>;
// Mapping: index pair -> coefficient of type T
template<typename T>
using dict2_t = std::map<std::tuple<indices_t,indices_t>,T>;
// Mapping: index quadruple -> coefficient of type T
template<typename T>
using dict4_t = std::map<std::tuple<indices_t,indices_t,indices_t,indices_t>,T>;
Here indices_t represents an operator index sequence (see fundamental_operator_set).
Coefficient extractors
Dictionary to matrix/tensor conversion