mat_rat Subroutine

subroutine mat_rat(x,len,maxd,a,b,d)

! ident_39="@(#)M_LA::mat_rat(3fp): A/B = continued fraction approximation to X using  len  terms each less than MAXD"

integer         :: len,maxd
doubleprecision :: x,a,b,d(len)
doubleprecision :: s,t,z
integer         :: i
integer         :: ib
integer         :: k
   z = x
   k=0  ! preset to illegal value
   if(len.lt.1)then
      write(*,*)'*mat_rat* internal error -- len<1'
      return
   endif
   do i = 1, len
      k = i
      d(k) = mat_round(z)
      z = z - d(k)
      if (dabs(z)*dble(maxd) .le. 1.0d0) exit
      z = 1.0d0/z
   enddo
   t = d(k)
   s = 1.0d0
   if (k .ge. 2) then
      do ib = 2, k
         i = k+1-ib
         z = t
         t = d(i)*t + s
         s = z
      enddo
   endif
   if (s .lt. 0.0d0) t = -t
   if (s .lt. 0.0d0) s = -s

   a = t
   b = s
end subroutine mat_rat