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library(bbmle)
library(deSolve)
dyn.load(“mymod.so”)
data4 = c(118, 154, 154, 182, 175, 190, 170, 147, 132, 149, 159, 175, 200, 217, 218, 228, 214, 217, 175, 139, 135, 131, 129, 124)
t4 = c(0:23)
base4 = c(112.6671, 113.8479, 114.9786, 116.0432, 117.0266, 117.9151, 118.6962, 119.3590, 119.8943, 120.2948, 120.5551, 120.6719, 120.6439, 120.4719, 120.1588, 119.7096, 119.1312, 118.4323, 117.6236, 116.7172, 115.7266, 114.6665, 113.5528, 112.4020)
model_SIR = function(t, theta) {
with(as.list(theta), { state1 = c(S = N - I1, I = I1) pars1 = c(beta = beta1, alpha = alpha1, N = N) state2 = c(S = N - I2, I = I2) pars2 = c(beta = beta2, alpha = alpha1, N = N) out1 = ode(y = state1, times = t, func = "derivs", parms = pars1, jacfunc = "jac", dllname = "mymod", initfunc = "initmod", nout = 1, outnames = "S") out2 = ode(y = state2, times = t, func = "derivs", parms = pars2, jacfunc = "jac", dllname = "mymod", initfunc = "initmod", nout = 1, outnames = "S") return(cbind(-diff(out1[,"S"]), -diff(out2[,"S"]))) })
}
loglik_negbin = function(theta, data, mean) {
# for negative bimonial, mean = r p /(1-p) r = theta[["r"]]; # if r < 0, return a tiny likelihood if (r < 0) { return(-1e10) } sum(dnbinom(x=data, size=r, mu=mean, log=TRUE))
}
SIR_fit_given_logL = function(times, data, base, theta0, model, logL) { # construct a general negative log-likelyhood function
L <- function() { # reconstruct the vector of named pairs of # parameters from the list of arguments l=length(theta0) theta=c() vars=names(theta0) for (i in 1:l) { item=c(x=get(vars[i])) names(item) <- vars[i] theta <-c(theta, item) } N = theta[["N"]] if(N < sum(data)) { return(1e10) } for(i in 1:length(theta)) { if(theta[[i]] < 0) { return(1e10) } } l = model(times, theta) #"base" is the vector of baseline values mean = l[,1] + l[,2] + base # compute the negative log-likelihood L = -logL(theta, data, mean) # if not a number, return a very small likelihood if (is.na(L)) { return(1e10) } return(L) }
# replace the input arguments of L by the list of parameters formals(L)←as.list(theta0) # mle2 # sometimes confint may find a better solution. # In this case we need to refit the model with the better # solution as a starting paoint, because the parameter # names in the returned better fit can be wrong fit = mle2(L, method = “BFGS”, start = as.list(theta0), control = list(maxit = 1e6*length(theta0))) # fit = mle2(L, method = “Nelder-Mead”, start = as.list(theta0), control = list(maxit = 1e6*length(theta0), ndeps = 1e-4, reltol = 1e-10)) # if there is only one parameter to be fitted # the returned confidence interval is a vector # change it to a matrix return(fit) }
SIR_fit = function(times, data, base, theta0, model) {
# we start with negative binomial if (is.na(theta0['r'])) { theta0 = c(theta0, r = 5000) } while (TRUE) { p = SIR_fit_given_logL(times, data, base, theta0, model, loglik_negbin) conf = confint(p) if(is.vector(conf)) { conf = matrix(conf, nrow = 1) } if(is.matrix(conf)) { break } theta0 = coef(conf) names(theta0) = names(coef(p)) } return(list(fit=p, conf = conf, r=coef(p)["r"]))
}
c = SIR_fit(c(0:24), data4, base4, c(beta1 = 4, alpha1 = 2.5, N = (sum(data4)*1.166), I1 = 1, beta2 = 1.2, I2 = 1), model_SIR)
print©
aicc = AICc(c"fit", nobs = length(data4))
print(aicc)