Function pm_one_compartment_with_absorption 

pub fn pm_one_compartment_with_absorption(
    x: &NalgebraVec<f64>,
    p: &NalgebraVec<f64>,
    t: f64,
    rateiv: &NalgebraVec<f64>,
    cov: &Covariates,
) -> NalgebraVec<f64>