Multiplicity function

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The multiplicity function Ω(n,N) is the same as the combinatoric function C(N,n). That is:

\Omega (n,N) = {N \choose n} = {{N!} \over {n!(N - n)!}}

It is primarily used in thermodynamics. If the multiplicity function represents a partially specified system of N particles where n are defined to be in one (of two) states, then the entropy of the system is given by the natural logarithm of the multiplicity function:

\sigma = \ln \Omega (n,N) \,