Function SCIPaddVarSOS2 

pub unsafe extern "C" fn SCIPaddVarSOS2(
    scip: *mut SCIP,
    cons: *mut SCIP_CONS,
    var: *mut SCIP_VAR,
    weight: f64,
) -> SCIP_RETCODE

adds variable to SOS2 constraint, the position is determined by the given weight