The QuEST API is divided into the following modules.

Unitaries	Unitary gates
Gates	Non-unitary but norm-preserving gates, such as measurements
Operators	Non-physical operators which may be non-unitary, non-norm-preserving, even non-Hermitian
Decoherence	Decoherence channels which act on density matrices to induce mixing
Data structures	Precision-agnostic types and data structures for representing numbers, quantum states, and operators
Calculations	Calculations and property-getters which do not modify the studied quantum state
State initialisations	Functions for preparing quantum states
QASM Logging	Functions for recording performed gates to QASM
Debugging	Utilities for seeding and debugging, such as state-logging
Unit tests	Unit tests of the QuEST API, using Catch2 in C++14
Unit test utilities	Functions used in the unit testing. These are mostly unoptimised, analytic implementations of the complex linear algebra that QuEST ultimately effects on quantum states. These are not part of the QuEST API, and require C++14