[MITgcm-devel] changes to very sensitive evp code

[Martin Losch]

Hi Jean-Michel and others,

for completeness, I'd like to implement the modified EVP* of Lemieux et al (2012). In order to be able to use the present (then old) EVP implementation, I have to introduce a few factors, etc. As you know, EVP is very sensitive to everything, so changing
SEAICEmassU/SEAICE_deltaTevp
to 
recip_deltaT = 1. _d 0 / SEAICE_deltaTevp
SEAICEmassU*recip_deltaT
already breaks the forward testreport for lab_sea.hb87 (only 2 digits of agreement left for the cg2d solver). Anything else that I do, does the same, eg. replacing
denom1 = 1./(1.+0.5*dt/tau)
with 
alph = 2*tau/dt
denom1 = alph/(alph+1)
has the same effect (in fact the difference between the two expressions is not zero but 1.110223e-16 on my linux computer)

Should I go ahead anyway and update the reference output? Can I ask you to update the adjoint, once I am done? EVP is not tested anywhere else.

Martin