[ecco-support] Budgets in ECv4, release 3

Mon Nov 6 12:08:19 EST 2017

Hi Martha, the non-random patterns in your figures
convince me that double precision is needed.

Cheers, Dimitris

On Nov 6, 2017, at 8:56 AM, Martha Buckley <marthabuckley at gmail.com<mailto:marthabuckley at gmail.com>> wrote:

I didn't chose the most instructive colorbar to show the magnitude of the errors. Attached are plots with colorbars to indicate the magnitude of the errors.  In particular, note that the errors due to single precision in the mass budget are on the order of 10% (saturated on the 1% colorbar).  Note these are the errors for a particular time step based on monthly output.

The issue with budgets with single precision output is that the tendancy is always a small residual of larger terms.  While of course the uncertainty of ECCO estimates is larger than even these 10% errors, I think this is not particularly relevant to this discussion.  ECCO in the end is also a forward model and MITgcm developers have take great pains to insure that budgets close.  I don't know why we'd sacrifice the ability to close budgets rigorously in order to save a factor of 2 in space by storing as single precision.   Also, for the user it is a lot easier if the budgets close to machine precision rather than having a user wonder if an error is "acceptable" or not.

Martha

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