integral that are a function of the parameters in our model. The arguments <code>x_r</code> and <code>x_i</code> are used to pass in real and integer arguments of the integral that are not a function of our parameters.</p>
<p>The function defining the integrand must have exactly the argument types and return type of <code>normal_density</code> above, though argument naming is not important. Even if <code>x_r</code> and <code>x_i</code> are unused in the integrand, they must be included in the function signa