OMP PRIVATE variable not initialised

[ukmo-ccbunney]

Describe the bug
In w3wavemd there is a NMIN variable used in an OMP loop that is PRIVATE, but it is not initialised. This could lead to undefined behaviour when running with OMP threading.

Loop is here:

WW3/model/src/w3wavemd.F90

Lines 3668 to 3674 in 488e3c8

	NMIN = NSEA
	!
	#ifdef W3_OMPG
	!$OMP PARALLEL PRIVATE (IPROC,NLOC,ISEA,JSEA,ISPROC,IXY,NMIN)
	!$OMP DO SCHEDULE (DYNAMIC,1)
	#endif
	DO IPROC=1, NAPROC

Use of potentially uninitialized value in the above loop is here:

WW3/model/src/w3wavemd.F90

Line 3692 in 488e3c8

NMIN = MIN ( NMIN , NLOC )

Proposed solution
I believe the problem should be resolved by using FIRSTPRIVATE(NMIN) in the OMP directive for that loop, i.e.:

!$OMP PARALLEL PRIVATE (IPROC,NLOC,ISEA,JSEA,ISPROC,IXY) FIRSTPRIVATE(NMIN) 

Additional context
I have not observed any undefined behaviour in OMP running of the SMC grid, but this is an example something that could catch us out in the future.

There may be other cases where we should be using FIRSTPRIVATE on variables for OMP loops too.

Related: #1017

[ukmo-ccbunney]

I'm raising this as an issue so we can keep track of it as I don't have time to fix this and run the regression tests before I down-tools for Xmas!