}}</ref> and hence they are of great importance to the physics of many-particle systems.
The HNC and PY integral equations provide the [[pair- distribution functionsfunction]]s of the particles in a classical fluid, even for very high coupling strengths. The coupling strength is measured by the ratio of the potential energy to the kinetic energy. In a classical fluid, the kinetic energy is proportional to the temperature. In a quantum fluid, the situation is very complicated as one needs to deal with quantum operators, and matrix elements of such operators, which appear in various perturbation methods based on [[Feynman]] diagrams. The CHNC method provides an approximate "escape" from these difficulties, and applies to regimes beyond perturbation theory. In [[Robert B. Laughlin]]'s famous Nobel Laureate work on the [[fractional quantum Hall effect]], an HNC equation was used within a classical plasma analogy.
In the CHNC method, the pair-distributions of the interacting particles are calculated using a mapping which ensures that the quantum mechanically correct non-interacting pair distribution function is recovered when the Coulomb interactions are switched off.<ref>
