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program standard_deviation
use grib_api
implicit none
character(len=100) :: file_name,out_file
integer :: ifile,ofile
integer :: igrib,ogrib
integer :: numberOfValues, nMessages
integer :: iret,i
real(8), dimension(:), allocatable :: values,sums,square_sums
! --- get input arguments
call getarg(1,file_name)
call getarg(2,out_file)
call grib_open_file(ifile,file_name,'r')
call grib_open_file(ofile,out_file,'w')
! --- count number of messages in grib
call grib_count_in_file(ifile,nMessages)
call grib_new_from_file(ifile,igrib,iret)
! --- create ouput grib from this one
call grib_clone(igrib,ogrib)
! --- get the number of values, we suppose all messages have
! - the same size for the sake of this example
call grib_get(igrib,'numberOfValues',numberOfValues)
! --- one should check if allocation was successfull
allocate(values(numberOfValues))
allocate(sums(numberOfValues))
allocate(square_sums(numberOfValues))
! --- compute the standard deviation
sums = 0
square_sums = 0
do while (iret/=GRIB_END_OF_FILE)
call grib_get(igrib,'values',values)
sums = sums + values
square_sums = square_sums + values * values
call grib_new_from_file(ifile,igrib,iret)
end do
sums = sums/nMessages
square_sums = square_sums/nMessages - sums*sums
do i=1,numberOfValues
if (square_sums(i) > 0.0) then
square_sums(i) = sqrt(square_sums(i))
else
square_sums(i) = 0.0
end if
end do
! --- write to the out file
call grib_set(ogrib,'values',square_sums)
call grib_write(ogrib,ofile)
! --- release mem
deallocate(values)
deallocate(sums)
call grib_release(igrib)
call grib_close_file(ifile)
call grib_close_file(ofile)
end program standard_deviation
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