The vector of velocities and normal stresses in a layer can be related to the amplitudes of the up- and downgoing waves by a block operator as shown in the appendix.

At a horizontal boundary between two layers the vectors and are continuous so we can write.I wish to calculate four reflection and transmission operators: In the appendix I show how to calculate the four reflection and transmission operators that my algorithm needs for steps three and five.

The operators *downrefl* and *downtrans* are the reflection and transmission
operators for a downgoing wave incident on an interface.

12/18/1997