ROMS/TOMS Developers

Algorithms Update Web Log

arango - July 26, 2006 @ 17:30
Updated 4DVAR Algorithms, Version 3.0- Comments (0)

I updated several files to facilitate IOM’s multiple executable option and 4D-PSAS:

  • Renamed couple of CPP options for clarity: REPRESENTERS to WEAK_CONSTRAINT and IOM_MULTIPLE to IOM. The WEAK_CONSTRAINT option is now used for weak constraint data assimilation options W4DVAR and W4DPSAS. The IOM option is now used exclusively to interface with IOM’s GUI.
  • Corrected a bug in obs_cost.F that affected the step size computation used in the IS4DVAR and S4DVAR conjugate gradient algorithm. We were actually only using the last observation time survey. We need sum over all time surveys.
  • I added the optimalilty property test from Weaver et al. (2002). This is a good diagnostic to check the consistency between background and observation error covariance hypotheses (Chi-square test). The cost function value at the minimum, Jmin, is ideally equal to half the number of observations assimilated for a linear system. That is, Optimality=2*Jmin/Nobs. The theoretical value for this normalized quantity is Optimality=1. Therefore, the closer to unity the better. This is only available in the IS4DVAR driver. To check for this quantity grep for Optimality in the standard output file.
  • I fine tunned obs_read.F and obs_write.F to report rejected observations counters (land/sea masking and out of bounds observations). This required some changes to variable ObsScale. I am very happy about this change. It makes more sense now.

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