Nodes of different colours represent the following:
Solid arrows point from a procedure to one which it calls. Dashed
arrows point from an interface to procedures which implement that interface.
This could include the module procedures in a generic interface or the
implementation in a submodule of an interface in a parent module.
public function init_integrator(num_gaussians, g_coords, g_exps, g_coefs, g_ams, g_lengths) bind(c, name="init_integrator")