Public repository of the Cosmic Linear Anisotropy Solving System (master for the most recent version of the standard code; GW_CLASS to include Cosmic Gravitational Wave Background anisotropies; classnet branch for acceleration with neutral networks; ExoCLASS branch for exotic energy injection; class_matter branch for FFTlog)
I calculated sigma^2 using the formula
$$\sigma^2(R) = \int_{0}^{\infty } \frac{P(k)k^2}{2\pi^2}W^2(kR)dk$$
where W is the top-hat window function. However, there is a discrepancy between the result and the one directly calculated using CLASS, specifically around R less than ~1 Mpc/h. Does anyone know the reason behind this?
I know the reason. The integral upper limit of k is not infinite in actual operation, so it will make a difference in small scales.
I calculated sigma^2 using the formula $$\sigma^2(R) = \int_{0}^{\infty } \frac{P(k)k^2}{2\pi^2}W^2(kR)dk$$
where W is the top-hat window function. However, there is a discrepancy between the result and the one directly calculated using CLASS, specifically around R less than ~1 Mpc/h. Does anyone know the reason behind this?
I know the reason. The integral upper limit of k is not infinite in actual operation, so it will make a difference in small scales.