= Smoothed matter density variance
{title2=$\sigma^2(M,z)=\frac1{2\pi^2}\int_0^\infty k^2P(k,z)|W(kR)|^2\,dk$}
= Cosmological mass variance
{synonym}
The <smoothed matter density variance> measures the root-mean-square linear <density contrast> after applying a window corresponding to a Lagrangian mass scale. For a homogeneous isotropic field it is $\sigma^2=(1/(2\pi^2))\int k^2P(k)|W(kR)|^2dk$. The variance convention, growth epoch and smoothing mass-density relation must agree with the collapse barrier used in a halo abundance calculation.
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