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# Talk:TAU0

## Notes from code dive

I dug through the code, came up with some inner workings that aren't documented. The following info needs to be added:

• spatially-averaging is done to tau0 in: SUBROUTINE CalculateTimeVaryingTau0(TK, NNeigh, NeiTab, NP)
• I see Casey's fingerprints
• tau0=-3, -5, -6, -7: looks to average tau0 across all immediate (?) nodal neighbors
• Rick said tau0=-5 is ineffective
• tau0=-3: the actual tau0 is capped at 0.2
• tau0=-6 is a time-averaging:

C jgf47.33 Perform time averaging of tau0 if requested.

```     IF (TimeAveragedTau0) THEN
DO I=1, NP
TAU0VAR(I) = 0.5d0*TAU0VAR(I) + 0.5d0*LastTau0(I)
LastTau0(I) = TAU0VAR(I)
ENDDO
ENDIF
```

• tau0=-7 is a different time-averaging:

C jgf48.42 Perform backloaded time averaging of tau0 if requested.

```     IF (BackLoadedTimeAveragedTau0) THEN
DO I=1, NP
TAU0VAR(I) = AlphaTau0*TAU0VAR(I)
&                 + (1.d0-AlphaTau0)*LastTau0(I)
LastTau0(I) = TAU0VAR(I)
ENDDO
ENDIF
```
• AlphaTau0 is hard-coded to 0.25, so 75% last tau0, 25% current one

T\$Taylorgasher (talk) 00:10, 16 February 2019 (UTC)

OK, done.Taylorgasher (talk) 13:49, 19 February 2019 (UTC)

## Undocumented TAU0 and nodal attribute interactions

In digging through the code, I've found there are very few behavior checks on a user's selection of TAU0 (fort.15) and either of the two nodal attributes. The only thing that's blocked (as far as I can tell) is setting TAU0=-3 or -6, and not specifying PWICE. I'm mostly not getting into any of the specifics on this stuff, but just wanted to denote that it's here.Taylorgasher (talk) 13:52, 19 February 2019 (UTC)