!-------------------------------------------------------------------------
      subroutine bilinear(x_arr,y_arr,nX,nY,f2d_arr,x_in,y_in,f)
!     Necessary for interpolation of continuum data

      implicit none

      integer nX,nY,i,j,a,b

      real*8 x_in,y_in,x,y,x1,x2,y1,y2
      real*8 f,f11,f12,f21,f22,fA,fB
      real*8 x_arr(nX)
      real*8 y_arr(nY)
      real*8 f2d_arr(nX,nY)
      
      integer strlen
      character*100 label
      label='subroutine bilinear'

      x=x_in
      y=y_in

!     1st check we're within the wavenumber range
      if ((x.lt.x_arr(2)).or.(x.gt.x_arr(nX-2))) then
         f=0.0D+0
         return
      else
         
!     in the x (wavenumber) direction 1st
         i=1
 10      if (i.lt.(nX+1)) then
            if (x_arr(i).gt.x) then
               x1=x_arr(i-1)
               x2=x_arr(i)
               a=i-1
               i=9999
            endif
            i=i+1
            goto 10
         endif
      endif
      
      if ((y.lt.y_arr(1)).or.(y.gt.y_arr(nY))) then
         write(*,*) 'Warning from bilinear.for:'
         write(*,*) 'Outside continuum temperature range!'
         if(y.lt.y_arr(1))then
            y=y_arr(1)+0.01
         endif
         if(y.gt.y_arr(nY))then
            y=y_arr(nY)-0.01
         endif
      else

!     in the y (temperature) direction 2nd
         j=1
 20      if (j.lt.(nY+1)) then
            if (y_arr(j).gt.y) then
               y1=y_arr(j-1)
               y2=y_arr(j)
               b=j-1
               j=9999
            endif
            j=j+1
            goto 20
         endif
      endif
      
      f11=f2d_arr(a,b)
      f21=f2d_arr(a+1,b)
      f12=f2d_arr(a,b+1)
      f22=f2d_arr(a+1,b+1)
      
!     1st in x-direction
      fA=f11*(x2-x)/(x2-x1)+f21*(x-x1)/(x2-x1)
      fB=f12*(x2-x)/(x2-x1)+f22*(x-x1)/(x2-x1)
      
!     then in y-direction
      f=fA*(y2-y)/(y2-y1)+fB*(y-y1)/(y2-y1)
      
      return
    end subroutine bilinear