The authors are grateful to M. L. Norman, J. M. Stone and D. A. Clarke for providing them with the ZEUS-2D package. They are especially indebted to R. Fiedler for his help in implementing the code. The cyclic reduction algorithm was provided by P. Swarztrauber. Thanks are also due to V. Pizzo for several illuminating discussions.
© European Southern Observatory (ESO) 1997
Online publication: April 6, 1998