# Calculating domain average of a variable

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#### flaounas

##### New member
Hello,

For a certain diagnostic, I have introduced to the registry a variable named "diag8". At every model time step, now I need to calculate the average of diag8 within the whole domain. For this reason I naively introduced the following piece of code at the beginning of "solve_em.F". Obviously this is not the correct way to do it since I am getting "meanval" equal to NaN :-|.

Could I please ask you for any tips on how to calculate the domain average of a certain variable?

Thank you in advance,
Manos

!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
!\$OMP PiRALLEL DO &
!\$OMP PRIVATE ( ij ) REDUCTION (+:meanval)
REDUCTION
DO ij = 1 , grid%num_tiles
DO i=ims,ime
DO k=kms,kme
DO j=jms,jme
meanval = meanval + abs(grid%diag8(i,k,j))/(ide*jde*kte)
END DO
END DO
END DO
END DO
!\$OMP END PARALLEL DO
!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

Hi,
Unfortunately I'm not a software engineer, and it looks like the only place domain-averaging is currently computed in the model is in the phys/module_diag_misc.F file. I'd recommend taking a look in the file to see how it was done for some of the other variables and try to do something similar. You may have to search the code a bit to determine how all the related variables are set-up.

Hi,

thank you for the answer. This was very helpful!

Looking into the file you mentioned helped me realize that wrf has a subroutine that calculates sums of variables treated by different processors (wrf_dm_sum_real).

Kind regards,
Manos

Manos,
That's great, and I'm glad I was able to provide at least a little help!