====== positions_principal ======

The integer parameter positions_principal defines the range around resonances for which a special integration treatment is used.

If the integration along the parallel axis is within position_principal steps of the real part of the resonance momentum, the one-sided resonance scheme is applied, as long as the resonance is within the integration domain and more than positions_principal steps away from the rim of the integration domain.

If a resonance is within positions_principal steps from the rim of the integration domain in the parallel direction, the integration excludes positions_principal steps from the resonance.

If a resonance is outside of the integration domain in the parallel direction but within positions_principal steps from the rim, the integration excludes positions_principal steps from the resonance.

positions_principal is part of the namelist &system.