| ssa.btl {GillespieSSA} | R Documentation |
Binomial tau-leap method implementation of the SSA as described by Chatterjee et al. (2005). It is usually called from within ssa, but can be invoked directly.
ssa.btl(x = stop("missing state vector (x)"),
a = stop("missing propensity vector (a)"),
nu = stop("missing state-change matrix (nu)"),
f = stop("missing coarse-graining factor (f)"))
x |
state vector. |
a |
vector of evaluated propensity functions. |
nu |
state-change matrix. |
f |
coarse-graining factor (see page 4 in Chatterjee et al. 2005). |
Performs one time step using the Binomial tau-leap method. Intended to be invoked by ssa.
A list with two elements, 1) the time leap (tau) and 2) the realized state change vector (nu_j).
Chatterjee et al. (2005)
a = function(parms,x){
b <- parms[1]
d <- parms[2]
K <- parms[3]
N <- x[1]
return(c(b*N , N*b + (b-d)*N/K))
}
parms <- c(2,1,1000,500)
x <- 500
nu <- matrix(c(+1, -1),ncol=2)
t <- 0
for (i in seq(100)) {
out <- ssa.btl(x,a(parms,x),nu,f=10)
x <- x + out$nu_j
t <- t + 1
cat("t:",t,", x:",x,"\n")
}