sfclayrev fix for divide by zero

[dudhia]

TYPE: bug fix

KEYWORDS: sfclayrev scheme, divide by zero

SOURCE: internal (reported by CH Liu)

DESCRIPTION OF CHANGES:
During iterative solution for z/L there are rare cases where the same bit-for-bit value is returned for slightly different inputs to function zolri2 resulting in a divide by zero. This appears to be rare.
Fix is to return when these are found equal because solution is converged already.

LIST OF MODIFIED FILES:
phys/module_sf_sfclayrev.F

TESTS CONDUCTED:
Fix works for case that stopped.
Test on standard June case is bit-for-bit as expected
No regtests yet (Jenkins?)

RELEASE NOTE:
Fix for occasional divide-by-zero error in sfclayrev option.

[weiwangncar]

@dudhia If we do a test, say the Jan 2000 case, would you get bit-for-bit results with this change?

[dudhia]

Very likely yes. It should only affect runs that stopped before.

…

On Wed, Dec 11, 2019 at 11:13 AM weiwangncar ***@***.***> wrote: @dudhia <https://github.com/dudhia> If we do a test, say the Jan 2000 case, would you get bit-for-bit results with this change? — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub <#1029?email_source=notifications&email_token=AEIZ77CXGKOK4PB2IGKQPYLQYEUTFA5CNFSM4JZGDFI2YY3PNVWWK3TUL52HS4DFVREXG43VMVBW63LNMVXHJKTDN5WW2ZLOORPWSZGOEGUCIXA#issuecomment-564667484>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AEIZ77BOXI3OYSX7SL4TPODQYEUTFANCNFSM4JZGDFIQ> .

[weiwangncar]

@dudhia Thanks. Could you do a test to verify this?

[dudhia]

test of June 2001 case gives bit4bit same results with fix as expected

[weiwangncar]

@dudhia That's good to know. I'm ok with the fix.