Gsum bug

[eclare108213]

Gsum is the cumulative area of ice and open water in a grid cell. It is occasionally 0 and causes a divzero error, though probably not in active grid cells. Fixing it may cause nonBFB results and therefore this will need to be tested in the full CICE model, once the new version of Icepack is added there.

[eclare108213]

Unfortunately this problem only shows up with some compilers, and I'm not seeing it so can't debug it. Hints for fixing it:

The issue occurs in this line, in icepack_mechred.F90:

 work = c1 / Gsum(ncat)

Gsum(ncat) should never be zero, so there is a problem somewhere else, maybe in a halo cell? The quick fix is to wrap this statement with "if (Gsum(ncat) > puny) then ... endif" but that does not fix the source of the problem.

[apcraig]

I've implemented this on a branch and am testing. PR soon.

[eclare108213]

PR #127 provides a work-around, but there is still an underlying bug. Gsum should never be zero. I am leaving this issue open for now, to return to later when more pressing issues have been addressed.