A modification introduced in the damped least-squares method automatically assigns a damping factor to each parameter in a manner that compensates for the relative sensitivities of the variables. The convergence rate of the lens-design process is thereby considerably improved. The operation of the program is described, in particular the use of Lagrangian undetermined multipliers for the control of boundary conditions.
JOSEPH MEIRON, "Damped Least-Squares Method for Automatic Lens Design," J. Opt. Soc. Am. 55, 1105-1107 (1965)