subroutine get_branch_inv_matrix(lat,mat,mat_forward, nbranch)

  use bmad
  implicit none
  type (lat_struct), target :: lat
  type (branch_struct), pointer :: branch ! ring  
  type (ele_struct) ele
  real(rp) mat(6,6),m(6,6), mat_forward(6,6)
  real(rp) temp(6,6)
  real(rp) test(6,6)
  integer nbranch, n_loc,n
  integer i
  integer j
  logical err

  temp = 0.
  forall(i=1:6)temp(i,i) = 1.
  
  
   branch => lat%branch(nbranch)

   do i = 1, branch%n_ele_track
     m = matmul(branch%ele(i)%mat6, temp)
     temp= m


!   do j=1,6
!    print '(6es12.4)', branch%ele(i)%mat6(j,1:6)
!   end do
    n=i
    if(index(branch%ele(i)%name,'INFA')/= 0)exit
   end do   
   print '(/,a,1x,i10,1x,a)', 'get_branch_inv_matrix at:',n, branch%ele(n)%name
   mat_forward = m
   call invert_matrix(m)

   mat = m
   
   test = matmul(mat,temp)

   print '(/,a)', 'test'
   do j=1,6
    print '(6es12.4)', test(j,1:6)
   end do

   return
   end