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        SUBROUTINE PERCELL(NUMERO,II,JJ,VALUE,CMNFLD,FLAG)
CNG This is a stand-alone subroutine to find and
CNG average observations for same cells.
CNG It takes in a number (NUMERO) of values (VALUE) 
CNG at [II,JJ] locations (possibly not unique), including
CNG a common field (CMNFLD, defined for all [II,JJ] but
CNG should be the same for common ones).
CNG It then averages values at common cells, ignoring flagged
CNG values (=FLAG), and carrying over CMNFLD.
CNG It finally returns the redefined set as:
CNG NUMERO=number of unique cells
CNG [II,JJ]=I,J locations of the unique cells
CNG VALUE=averaged values at the unique cells.
CNG Note that the algorithm is designed to retain all
CNG unique cells, includines ones with values that are all
CNG flagged (and are ignored for averaging).
CNG Nickitas Georgas, 05/06/2008

        integer NUMERO
        real FLAG
	real VALUE(NUMERO),VALOUT(NUMERO)
        real CMNFLDO(NUMERO),CMNFLD(NUMERO)
        integer ICNT(NUMERO),INDX(NUMERO)
        integer II(NUMERO),JJ(NUMERO)
        integer IOUT(NUMERO),JOUT(NUMERO)

        IUNQ=1
        do n=1,NUMERO
         VALOUT(n)=0.0
         INDX(n)=N
         ICNT(n)=1
         IOUT(n)=0
         JOUT(n)=0
        enddo
        IUNQ=NUMERO
        do n=1,NUMERO-1
         do m=n+1,NUMERO
          if (II(m).eq.II(n).and.JJ(m).eq.JJ(n)) then
           ICNT(M)=0
           if (INDX(n).ne.N) then
            INDX(m)=INDX(n)
           else
            ICNT(N)=ICNT(N)+1
            INDX(M)=N
            IUNQ=IUNQ-1
           endif
          endif
         enddo
        enddo
        do n=1,NUMERO
         if (VALUE(n).eq.FLAG) then
          ICNT(INDX(n))=ICNT(INDX(n))-1 ! Do not average flagged data
         endif
         iout(INDX(n))=ii(n)
         jout(INDX(n))=jj(n)
         CMNFLDO(INDX(n))=CMNFLD(n)
        enddo
        do n=1,NUMERO
         if (VALUE(n).ne.FLAG)
     +    VALOUT(INDX(n))=VALOUT(INDX(n))+VALUE(n)/float(ICNT(INDX(n)))
        enddo
CNG        write (*,'(2(f10.2,2i5))')
CNG     +  (VALUE(n),ICNT(n),INDX(n),VALOUT(n),iout(n),jout(n),
CNG     +n=1,NUMERO)
        m=0
        do n=1,NUMERO
         if (ICNT(n).eq.0) then 
          VALOUT(n)=FLAG
         endif
         m=m+1
         if (IOUT(n).eq.0.and.JOUT(n).eq.0) then
          m=m-1
         else
          VALOUT(m)=VALOUT(n)
          iout(m)=iout(n)
          jout(m)=jout(n)
          CMNFLDO(m)=CMNFLD(n)
         endif
        enddo
CNG        write (*,*) '---'
CNG        write (*,'(2f10.2,2i5)')
CNG     +   (VALOUT(n),CMNFLDO(n),iout(n),jout(n),n=1,m)

        NUMERO=IUNQ
        do n=1,NUMERO
         VALUE(n)=VALOUT(n)
         ii(n)=iout(n)
         jj(n)=jout(n)
         CMNFLD(n)=CMNFLDO(n)
        enddo
        
        return
        end