Lower-triangular-like matrix \(\sigma(x)\) such that
\(\sigma(x)\sigma(x)^\top = \Sigma(x)\), driven by a 3-dimensional
Brownian motion with one independent noise channel per elementary event.
Usage
sird_sigma(state, parms)
Arguments
state
Numeric vector c(s, i, r).
parms
Named numeric vector/list with elements lambda, gamma, alpha.
