Function algorithm_x_bounds 

pub fn algorithm_x_bounds(
    nlp: &dyn IpoptNlp,
    x: &[Number],
) -> (Vec<Number>, Vec<Number>)

The variable bounds nlp iterates against — its live x_L / x_U, i.e. the declared box after bound_relax_factor widened it and any safe-slack adjustment moved it (upstream IpoptNLP::x_L(), what curr_slack_x_L is measured to) — in the shape of the TNLP it wraps (UserIterate::x_l_alg): ±∞ at a column with no such bound, and at a fixed variable the algorithm does not hold, its value x[j].