= Radial distribution function
{title2=$dN_r=4\pi n r^2g(r)\,dr$}
In a homogeneous isotropic one-component fluid, $g(r)$ is the conditional <number density> at separation $r$ from a tagged particle divided by the bulk number density $n$. Thus the displayed shell contains the mean number of neighbours. For an uncorrelated ideal gas $g(r)=1$ away from the tagged particle; repulsive cores suppress small separations, while liquid coordination shells can produce damped oscillations approaching one at large distance. This is a pair correlation, not a normalized one-particle radial probability density. The <static structure factor> measures its Fourier-space counterpart.
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