Consider revising the formulation of the pressure level interpolation in the ECMWF state-to-state codes

[Ian Culverwell]

Stig Syndergaard (DMI) has discovered that the calculation of full level pressures and geopotentials in ropp_fm_state2state_ecmwf.f90, and its TL and AD counterparts, can be expressed more simply and elegantly than at present. See r6130.

I suggest that this change be used to practise the new way of developing ROPP in CDOP4 (see https://trac.romsaf.org/ropp/browser/ropp_doc/trunk/ROPP_development_in_CDOP4.pdf).

This procedure involves the following steps.

• The owner of the change (probably Stig in this case) needs to provide:
  1. a justification for the change, and
  2. the names of people who have agreed to develop and review the change.

• The developer needs to do the following.
  1. Take a development branch off the trunk, to contain the work.
  2. Carry out developments on the branch.
  3. Test the change and document the test results on the ticket.
  4. If the development involves new science, then:
     1. put the change on a switch, and
     2. write a new test of this change, which will be included in the set of automatic daily build tests (which are to be introduced in CDOP-4).
  5. Write and document the change, e.g. for ROPP user guides, overview, change log, release notes etc, and upload to ticket.

• The reviewer (or reviewers) needs (or need) to examine the change and its documentation, based on the evidence on the ticket.

• There can be some to-and-fro between the reviewer and the developer, until the reviewer finally either accepts or declines the change.

• If the change is accepted, the developer or the ROPP development manager (to be decided) commits the change to the trunk.