!This subroutine fills gaps in the y variable based on neural network regression
      subroutine gapfilling(nx,nobs,xsamp,ysamp,nmax,maxdist)
      implicit none
!Gaps must be represented by -9999
!It is ok to have missing values in xsamp. If any dimension in xsamp is missing, that dimension
!is not used as the independent variable for the gap in y. For different gaps in y, the dimensions used
!in x may be different.
!If a gap is less than maxdist points away from a previous gap for which a fit was conducted and if
!the dimension is the same, then the previous fit is used (a new fit is not conducted) 
      integer nx,nobs,nmax
      double precision xsamp(1:nobs,1:nx),ysamp(1:nobs)
!Locals
      integer i,j,k,n,idowhat,nh,nxfit,nobsfit,negobsfit,ixuse(nx),
     &ipregap,iposfit(-nmax:nmax),iuseit,ixuse_pre(nx),maxdist
      parameter(nh=15)
      double precision w(1:nx,1:nh),bph(nh),q(nh),bend,
     &xnew(nx),calvalue(nobs),fn9999,tiny,xfit(-nmax:nmax,nx),
     &yfit(-nmax:nmax),rsq,ysamppred(nobs)
      parameter(fn9999=-9999.0d0,tiny=1.0d-6)
!
      bend=fn9999
      ipregap=-100000
      do i=1,nobs
        ysamppred(i)=ysamp(i)
        if(dabs(ysamp(i)-fn9999).gt.tiny)goto 1000
!a gap
        nxfit=0
        do j=1,nx
          if(dabs(xsamp(i,j)-fn9999).lt.tiny)then
!this x dimension is not used
            ixuse(j)=0
          else
!this x dimension is used
            nxfit=nxfit+1
            xnew(nxfit)=xsamp(i,j)
            ixuse(j)=1
          endif
        enddo
        if(nxfit.eq.0)goto 1000
        if((i-ipregap).lt.maxdist)then
          iuseit=1
          do j=1,nx
            if(ixuse(j).ne.ixuse_pre(j))iuseit=0
          enddo
          if(iuseit.eq.1)goto 30
        endif

!Fill this gap by choosing the nmax valid points that are closest to i for the fitting
!First pick up nmax points from the lower side, index positive
        nobsfit=0
        n=i-1
1       if(n.lt.1)goto 2
        if(dabs(ysamp(n)-fn9999).gt.tiny)then
          iuseit=1
!make sure it has the x dimensions needed
          do j=1,nx
            if(ixuse(j).eq.1)then
              if(dabs(xsamp(n,j)-fn9999).lt.tiny)iuseit=0
            endif
          enddo
          if(iuseit.eq.1)then
            nobsfit=nobsfit+1
            yfit(nobsfit)=ysamp(n)
            iposfit(nobsfit)=n
            k=0
            do j=1,nx
              if(ixuse(j).eq.1)then
                k=k+1
                xfit(nobsfit,k)=xsamp(n,j)
              endif
            enddo
          endif
        endif
        if(nobsfit.lt.nmax)then
          n=n-1
          goto 1
        endif
!
!now pick up nmax points form the higher side, index negative
2       negobsfit=1
        n=i+1
3       if(n.gt.nobs)goto 4
        if(dabs(ysamp(n)-fn9999).gt.tiny)then
          iuseit=1
!make sure it has the x dimensions needed
          do j=1,nx
            if(ixuse(j).eq.1)then
              if(dabs(xsamp(n,j)-fn9999).lt.tiny)iuseit=0
            endif
          enddo
          if(iuseit.eq.1)then
            negobsfit=negobsfit-1
            yfit(negobsfit)=ysamp(n)
            iposfit(negobsfit)=n
            k=0
            do j=1,nx
              if(ixuse(j).eq.1)then
                k=k+1
                xfit(negobsfit,k)=xsamp(n,j)
              endif
            enddo
          endif
        endif
        if(negobsfit.gt.-nmax)then
          n=n+1
          goto 3
        endif

!finally pick up the nmax closest points
4       if((nobsfit-negobsfit+1).le.nmax)goto 10
        if((i-iposfit(nobsfit)).gt.(iposfit(negobsfit)-i))then
          nobsfit=nobsfit-1
        else
          negobsfit=negobsfit+1
        endif
        goto 4
10      do n=negobsfit,0
          nobsfit=nobsfit+1
          yfit(nobsfit)=yfit(n)
          do j=1,nxfit
            xfit(nobsfit,j)=xfit(n,j)
          enddo
        enddo
        idowhat=1
        call NeuralNetRegres(idowhat,nxfit,nobsfit,nh,
     &xfit(1:nobsfit,1:nxfit),yfit,calvalue,rsq,
     &w(1:nxfit,1:nh),bph,q,bend,xnew,ysamppred(i:i))

        do j=1,nobsfit
          write(122,*)j,yfit(j),calvalue(j)
        enddo

        ipregap=i
        do j=1,nxfit
          ixuse_pre(j)=ixuse(j)
        enddo
30      idowhat=2
        call NeuralNetRegres(idowhat,nxfit,1,nh,
     &xfit(1:1,1:nxfit),yfit,calvalue,rsq,
     &w(1:nxfit,1:nh),bph,q,bend,xnew,ysamppred(i:i))
1000    continue
      enddo
      do i=1,nobs
        ysamp(i)=ysamppred(i)
      enddo
300   format(10f16.8)
      return
      end subroutine gapfilling