“…Approximating the partial derivatives using finite differences and using equation (19), equations (30) and (31) are written in terms of the unknowns ψ p , ψ' f and ω f on AB, ψ' f and ω' f on BCDA and the knowns ψ f and ω f on BCDA . Hence equations (28), (30) and (31) give 2N f +N p equations in the 2N f +N p unknowns: ψ p , ψ' f and ω f on AB ψ' p on BFEA ψ' f and ω' f on BCDA These were solved and then the complete boundary information on AB obtained, using equation (19) to obtain ψ f , equation (26) to obtain ψ' p , and equation (22) to obtain ω' f .…”