Function SCIPaddExprNonlinear 

pub unsafe extern "C" fn SCIPaddExprNonlinear(
    scip: *mut SCIP,
    cons: *mut SCIP_CONS,
    expr: *mut SCIP_EXPR,
    coef: f64,
) -> SCIP_RETCODE

adds coef * expr to nonlinear constraint

@attention This method can only be called in the problem stage.