program chi_square_sum
!**********************************************************************
! *              .      .    .
! * PROGRAM:    CHI_SQUARE_SUM
! * PRGMMR:     M. ZUPANSKI     ORG: CIRA/CSU   DATE: 2003-10-21
! *
! * ABSTRACT:   CALCULATE INNER PRODUCT BETWEEN TWO VECTORS
! *             SUM OVER ALL OBS CATEGORIES
! *
! * PROGRAM LOG:
! *
! * 10/21/2003    ..... M. ZUPANSKI:
! * 01/02/2004    ..... M. ZUPANSKI: moving average added
! * 09/08/2004    ..... M. ZUPANSKI: single program for obs and model chi-square
! * 09/08/2004    ..... M. ZUPANSKI: on-the-fly chi-square
! *
! **********************************************************************
!----------------------------------
!   INPUT:
!         product - inner product: (x_1**T)*x_1
!
!  OUTPUT: 
!         product_sum - total chi square (sum)
!
!----------------------------------
!-----
     integer,parameter::inner=21          ! input file #
     integer,parameter::chi_sum=51      ! input-output file #
!-----
     integer :: N_dim,N_sum

     real :: product
     real :: product_sum
     real,dimension(:),allocatable::x_1
     logical :: file_exist
     character*1 categ
!-----
!==============start calculation===================
!-- read innov file
     rewind inner
     read(inner) N_dim
     allocate(x_1(1:N_dim))
     read(inner) x_1

       product=0.0
        do i=1,N_dim
       product=product+x_1(i)*x_1(i)
        end do

      deallocate(x_1)

 100  format(I15,E20.10)

!---- read previous sum of chi_squares  -------
!     call getenv("icateg",categ)
!     write(*,*) "Current category=",categ

!     if(categ.eq.'1') then
!      write(*,*) "Previous CHI_SUM file DOES NOT exist"
        N_sum=0
         product_sum=0.0
!     else
!      write(*,*) "Previous CHI_SUM file DOES exist"
        rewind chi_sum
         read(chi_sum,100,err=220) N_sum,product_sum
!     end if

!-- Inner product --------------------

  220   product_sum=float(N_sum)*product_sum + product
        N_sum=N_sum+N_dim
        product_sum=product_sum/float(N_sum)


      rewind chi_sum
      write(chi_sum,100) N_sum,product_sum

            end program chi_square_sum