SUBROUTINE retrieval_options_setup(
     & NCHN,ML,MGS,MDET,ngdo, NL, NDET, NREG, nsr, ner,
     & ZREG, ANER,VARY,  ZA,  ZSTART, ZEND, IEVENT,
     &  tran, mt, zoffsun)
c
c a function that will determine the array index which bounds a value
c
      external location

CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
C
C  sets up some retrieval options
C
CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
 
      LOGICAL IEVENT(ML,MGS,NCHN)
      REAL*8 tran(ml,mt)
      DIMENSION ZA(ml),VARY(ML,MDET,NCHN),ANER(NCHN,NDET),
     & ZSTART(MGS,NCHN),ZEND(MGS,NCHN)
 
      if( zreg .ge. 0.) then
          call location(za, nl, zreg, nreg)
c          if(nreg .eq. 0) nreg = 1
          if(nreg .eq. 0 .or. za(nreg) .ne. zreg) then 
             do i = nl, nreg+1, -1
               za(i+1)=za(i)
             enddo
             za(nreg+1) = zreg
             nreg=nreg+1
             nl=nl+1
          endif
      endif
      ner = 0
      nsr = nl + 1

      DO ICHN=1,NCHN
c         print*, aner(ichn,1)
        DO I=1,NL
          do j =1, ndet
             VARY(I,j,ICHN)=ANER(ICHN,j)**2
          enddo
          DO IG=1, ngdo
            IEVENT(I,IG,ICHN)=.FALSE.
            IF(ZSTART(IG,ICHN).GT.0.0.AND.(ZA(I).LE.ZSTART(IG,ICHN).AND.
     &         ZA(I).GE. max(ZEND(IG,ICHN),zoffsun) )) THEN
                  IEVENT(I,IG,ICHN)=.TRUE.
                  nsr = min(i, nsr)
                  ner = max(i, ner)
            endif
          ENDDO
        ENDDO
c        print*, vary(1,1,ichn)
      ENDDO
      do i1 = 1, mt
         do i2 = 1,ml
           tran(i2,i1) = -999.0
         enddo
      enddo

      WRITE(*,*) 'EXITING retrieval_options_setup.F, NSR,NER= ',
     &   Nsr,Ner
       write(*,*) za(nsr), za(ner) 
      RETURN
      END