# Operator Terms This module collects routines that operate on the individual terms of an operator, partitioning them based on their structure. The submodules below group related functionality. ## Grouping Please refer to [Group operator terms: use the operator structure](../guides/grouping.html.md#grouping-explanation) for a detailed explanation of this module’s functionality. ### Assignment Rather than always relying on the user to provide the group indices themselves, this module provides a collection of functions which determine the grouping information automatically. ### Analysis Group indices carry no intrinsic meaning: the array only says which terms belong together, never why. Accordingly, none of the functions below reports whether a grouping is “correct”: each answers one narrow, stated question about an existing grouping, leaving the interpretation to you. They are provided so that an assumption a downstream consumer makes about a grouping can be checked up front, rather than being paid for on every call. ## Filtering This module provides convenience functions for removing terms from an operator that do not contribute meaningfully to a downstream computation. ### Members ## Ordering This module provides functions to reorder the terms of an operator. While the resulting operators are mathematically identical, the term order can have significant implications on algorithm behavior at runtime, due to the term iteration order. Group indices are a per-term tag that says nothing about where those terms sit, so the terms of one group are in general scattered throughout an operator. [`group_order()`](../stubs/qiskit_fermions.operators.terms.group_order.html.md#qiskit_fermions.operators.terms.group_order) gathers each group into one contiguous run, which is what lets [`split_out_groups()`](../stubs/qiskit_fermions.operators.OperatorTrait.html.md#qiskit_fermions.operators.OperatorTrait.split_out_groups) locate a requested group by binary search instead of scanning every term. #### NOTE Unlike [`canonical_order()`](../stubs/qiskit_fermions.operators.terms.canonical_order.html.md#qiskit_fermions.operators.terms.canonical_order), [`order_terms()`](../stubs/qiskit_fermions.operators.terms.order_terms.html.md#qiskit_fermions.operators.terms.order_terms) has no counterpart in the C API. ### Members