Function build_ac_opf_preparation 

pub fn build_ac_opf_preparation(
    instance: &AcOpfInstance,
    options: &AcOpfAssemblyOptions,
) -> Result<AcOpfPreparation>

Derive the complete matrix free AC OPF arrays from the instance: demand, shunt, and voltage columns per bus, the full pi model per active branch, and generator costs, bounds, and schedules with their source row mapping. The AC counterpart of build_dc_opf_preparation.

Errors

A network the pi model cannot assemble: missing reference coverage, an unresolved zero impedance branch, or an unusable cost curve.