Helper objective function for finding a pair of optimal attack-rates for a given pair of starting prevalence rates when the model has an exposure class

Helper objective function for finding a pair of optimal attack-rates for a given pair of starting prevalence rates when the model has an exposure class

fn2(params, Tx, PAR, Bfn, X)

Arguments

params	A pair of attack-rates
Tx	A vector of case-management rates
PAR	A set of model parameters
Bfn	A function for building the matrix represention of the system of equations that update the state vector
X	A pair of prevalence rates