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Potential Cancellation Issue in deln_flux #323
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Hi, @oelbert. Thank you for identifying these changes from GMAO. Indeed this better representation of order-of-operations when computing flux divergences, which are done at a number of places in the solver, could go a long way to avoiding some of the cancellations that can occur. They also define the Flux Capacitors |
The d2 calculation near the end of deln_flux has discrepant results between 64- and 32-bit caulculations:
GFDL_atmos_cubed_sphere/model/tp_core.F90
Line 1316 in 9ca1468
The GEOS team has resolved this by enforcing the order-of-operations in the flux addition/subtractions:
d2(i,j) = ((fx2(i,j)-fx2(i+1,j))+(fy2(i,j)-fy2(i,j+1)))*gridstruct%rarea(i,j)
This could be a good improvement to 32-bit runs
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