[1] Werner, A. and Eliezer, J.C. (1969) The Lengthening Pendulum. Journal of Australian Mathematical Society, 9, 331-336. http://dx.doi.org/10.1017/S1446788700007254
[2] Littlewood, J.E. (1963) Lorentz’s Pendulum Problem. Annals of Physics, 21, 233-249.
http://dx.doi.org/10.1016/0003-4916(63)90107-6
[3] Littlewood, J.E. (1964) Adiabatic Invariance III. The Equation . Annals of Physics, 29, 1-12.
http://dx.doi.org/10.1016/0003-4916(64)90188-5
[4] Littlewood, J.E. (1964) Adiabatic Invariance IV: Note on a New Method for Lorentz’s Pendulum Problem. Annals of Physics, 29, 13-18. http://dx.doi.org/10.1016/0003-4916(64)90189-7
[5] Littlewood, J.E. (1964) Adiabatic Invariance V. Multiple Periods. Annals of Physics, 30, 138-153.
http://dx.doi.org/10.1016/0003-4916(64)90307-0
[6] Brearley, M.N. (1966) The Simple Pendulum with Uniformly Changing String Length. Proceedings of the Edinburgh Mathematical Society (Series 2), 15, 61-66.
[7] Sánchez-Soto, L.L. and Zoido, J. (2013) Variations on the Adiabatic Invariance: The Lorentz Pendulum. American Journal of Physics, 81, 57. http://dx.doi.org/10.1119/1.4763746
[8] Boas, M.L. (2006) Mathematical Methods in the Physical Science. 3rd Edition, Wiley, 598-599.
[9] Gil, A., Segura, J. and Temme, N. (2007) Numerical Methods for Special Functions. SIAM.
http://dx.doi.org/10.1137/1.9780898717822
[10] Garcia, A.L. (2000) Method for Physics. 2nd Edition, Prentice-Hall, NJ.