Vicelli, J. A. "Exponential Difference Operator Approximation for the Sixth Order Onsager Equation." J. Comput. Phys.50,
pp. 162-170, 1983.Wood, H. G. and Morton, J. B. "Onsager's
Pancake Approximation for the Fluid Dynamics of a Gas Centrifuge." J. Fluid
Mech.101, 1-31, 1980.Zwillinger, D. Handbook
of Differential Equations, 3rd ed. Boston, MA: Academic Press, pp. 128-129,
1997.