subroutine get_branch_inv_matrix(lat,mat,mat_forward, nbranch, err)

  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), diag_prod
  integer nbranch, n_loc,n
  integer i
  integer j
  logical err

  err=.false.
  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 .or. index(branch%ele(i)%name,'MIDWAY')/=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)', 'Branch 0 forward matrix'
   do j=1,6
    print '(6es12.4)', temp(j,1:6)
   end do
   print '(/,a)', 'Branch 0 inverse matrix'
   do j=1,6
    print '(6es12.4)', mat(j,1:6)
   end do
   print '(/,a)', 'test - mat*temp (should be identity)'
   do j=1,6
    print '(6es12.4)', test(j,1:6)
   end do
 !the matrix <test> should be the identity. And if it is then Prod test(i,i) = 1
 diag_prod = test(1,1) * test(2,2)* test(3,3)* test(4,4)* test(5,5)* test(6,6)
 if(abs(diag_prod -1.) > 0.1)err = .true.

 if(err) print '(/,a)', ' No inverse injection line matrix '

   return
   end