Adjoint radiation boundary conditions

[arango]

The radiation conditions are not trivial in adjoint codes since the radiation celerities for the basic (forward) state need to be saved for every 2D and 3D time-steps. In addition, it is tricky to keep the tangent linear and adjoint model stable under such boundary conditions. Therefore, we have ignored this type of boundary conditions in all adjoint-based algorithms.

Since we are not satisfied with this type of boundary conditions in the nonlinear code, we have not pay attention to this option in the TLM, RPM, and ADM codes. Some of the infrastructure for these options has been coded but not tested. We keep getting inquires about this options. We will look at this in the future.

Anyway, there are few bugs associated with adjoint radiation conditions. I am correcting some of these codes but still this option is not available!

You need to use a different strategy for open boundary conditions in the adjoint-based algorithms. Many thanks to all of you who inquired about this.

[arango]

I also corrected typo in ad_zetabc.F line 99:

use
      ad_Cx=0.0_r8
instead of 
      ad_Ce=0.0_r8

Many thanks to Gordon Zhang for finding this one.