D. Feit and J. A. Fleck, Riazuelo, Ph.D. thesis in French 13 The maximum of the function C has been calculated by precisely locating the maximum, via a dichotomy method; a two-mesh interval has been used along every direction around a first indication of the mesh where C maximizes , with use of the seventh-order Lagrange interpolation function, J. Opt. Soc. Am. B, vol.5, issue.633, 1988.