Analytical solution of covariance evolution for regular LDPC codes

The covariance evolution is a system of differential equations with respect to the covariance of the number of edges connecting to the nodes of each residual degree. Solving the covariance evolution, we can derive distributions of the number of check nodes of residual degree 1, which helps us to estimate the block error probability for finite-length LDPC code. Amraoui et al. resorted to numerical computations to solve the covariance evolution. In this paper, we give the analytical solution of the covariance evolution.