Function for accessing the external GSL QAGS integration routine, which is limited to the 21-point GK routine, but can handle singularities in the region of integration.
Keep in mind that the 'integrand' must be "created" beforehand: see the 'CreateIntegrand' model and the 'integrand_setup' function.
function qags
extends Modelica.Icons.Function;
input Integer n_par;
input Real par[n_par], a, b, rel_err;
input Integer limit;
output Real y, err;
end qags;