subroutine digraph_adj_example_abc ( A )

!*****************************************************************************80
!
!! digraph_adj_example_abc() sets up the adjacency matrix associated with a network.
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    10 April 2026
!
!  Author:
!
!    John Burkardt
!
!  Output:
!
!    integer A(3,3): an adjacency matrix.
!
  implicit none

  integer, parameter :: node_num = 3

  integer A(node_num,node_num)

  A = reshape ( (/ &
     0, 1, 0, &
     0, 0, 1, &
     1, 0, 0 /), (/ node_num, node_num /) )

  A = transpose ( A )

  return
end
subroutine digraph_adj_example_abcd ( A )

!*****************************************************************************80
!
!! digraph_adj_example_abcd() sets up the adjacency matrix associated with a network.
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    10 April 2026
!
!  Author:
!
!    John Burkardt
!
!  Output:
!
!    integer A(4,4): an adjacency matrix.
!
  implicit none

  integer, parameter :: node_num = 4

  integer A(node_num,node_num)

  A = reshape ( (/ &
     0, 1, 0, 0,  &
     0, 0, 1, 0,  &
     1, 0, 0, 1,  &
     1, 0, 0, 0/), (/ node_num, node_num /) )

  A = transpose ( A )

  return
end
subroutine digraph_adj_example_cycler ( A )

!*****************************************************************************80
!
!! digraph_adj_example_cycler() sets adjacency information for the cycler digraph.
!
!  Diagram:
!  
!           A
!           V
!    9--><--7---<--3--><---4
!    |            /|      /
!    V           A |     /
!    |          /  |    /
!    5----<----1   V   A
!    |        /    |  /
!    V       A     | /
!    |      /      |/
!    2-->---8---<--6
!     \------>----/
!
!  Licensing:
!
!    This code is distributed under the MIT license. 
!
!  Modified:
!
!    22 October 1999
!
!  Author:
!
!    John Burkardt
!
!  Output:
!
!    integer A(9,9), the adjacency information.
!    ADJ(I,J) is 1 if there is a direct link from node I to node J.
!
  implicit none

  integer, parameter :: node_num = 9

  integer A(node_num,node_num)

  A(1:node_num,1:node_num) = 0

  A(1,3) = 1
  A(1,5) = 1

  A(2,6) = 1
  A(2,8) = 1

  A(3,4) = 1
  A(3,6) = 1
  A(3,7) = 1

  A(4,3) = 1

  A(5,2) = 1

  A(6,4) = 1
  A(6,8) = 1

  A(7,7) = 1
  A(7,9) = 1

  A(8,1) = 1

  A(9,5) = 1
  A(9,7) = 1

  return
end
subroutine digraph_adj_print ( A, node_num, title )

!*****************************************************************************80
!
!! digraph_adj_print() prints out an adjacency matrix for a digraph.
!
!  Discussion:
!
!    This routine actually allows the entries to have ANY value.
!    Values between 0 and 9 will be printed as is.  Other values will
!    be printed as '*'.
!
!  Licensing:
!
!    This code is distributed under the MIT license. 
!
!  Modified:
!
!    04 July 2000
!
!  Author:
!
!    John Burkardt
!
!  Input:
!
!    integer A(node_num,node_num), the adjacency matrix of a 
!    digraph.  A(I,J) is 1 if there is a direct connection FROM node I TO 
!    node J, and is 0 otherwise.
!
!    integer node_num: the number of nodes.  
!
!    character ( len = * ) TITLE, a title.
!
  implicit none

  integer node_num

  integer A(node_num,node_num)
  integer i
  integer j
  integer jhi
  character ( len = 80 ) string
  character ( len = * ) title

  if ( len_trim ( title ) /= 0 ) then
    write ( *, '(a)' ) ' '
    write ( *, '(a)' ) trim ( title )
  end if

  write ( *, '(a)' ) ' '

  do i = 1, node_num

    jhi = min ( node_num, 80 )

    do j = 1, jhi

      if ( 0 <= A(i,j) .and. A(i,j) <= 9 ) then
        string(j:j) = char ( 48 + A(i,j) )
      else
        string(j:j) = '*'
      end if

    end do

    write ( *, '(i2,2x,a)' ) i, string(1:jhi)

  end do

  return
end
subroutine digraph_adj_example_five ( A )

!*****************************************************************************80
!
!! digraph_adj_example_five() sets up the adjacency matrix associated with a network.
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    10 April 2026
!
!  Author:
!
!    John Burkardt
!
!  Output:
!
!    integer A(5,5): an adjacency matrix.
!
  implicit none

  integer, parameter :: node_num = 5

  integer A(node_num,node_num)

  A = reshape ( (/ &
     0, 1, 0, 0, 0,  &
     0, 0, 0, 0, 1,  &
     1, 0, 0, 0, 0,  &
     1, 0, 0, 0, 0,  &
     1, 0, 0, 0, 0 /), (/ node_num, node_num /) )

  A = transpose ( A )

  return
end
subroutine digraph_adj_example_moler ( A )

!*****************************************************************************80
!
!! digraph_adj_example_moler() returns the adjacency matrix for Moler's example 3.
!
!  Discussion:
!
!    This matrix appears on page 5 of the reference.
!
!    We added a self-link for node 5, which otherwise has no outlinks.
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    10 April 2026
!
!  Author:
!
!    John Burkardt
!
!  Reference:
!
!    Cleve Moler,
!    Experiments with Matlab,
!    Chapter 7: Google PageRank,
!    https://www.mathworks.com/moler/exm/chapters/pagerank.pdf
!
!  Output:
!
!    integer A(6,6), the adjacency matrix.
!
  implicit none

  integer, parameter :: node_num = 6

  integer A(node_num,node_num)

  A = reshape ( (/ &
     0, 1, 0, 0, 0, 1,  &
     0, 0, 1, 1, 0, 0,  &
     0, 0, 0, 1, 1, 1,  &
     1, 0, 0, 0, 0, 0,  &
     0, 0, 0, 0, 1, 0,  &
     1, 0, 0, 0, 0, 0/), (/ node_num, node_num /) )

  A = transpose ( A )

  return
end
subroutine digraph_adj_example_sauer ( A )

!*****************************************************************************80
!
!! digraph_adj_example_sauer() sets up the adjacency matrix associated with a network.
!
!  Licensing:
!
!    This code is distributed under the MIT license.
!
!  Modified:
!
!    10 April 2026
!
!  Author:
!
!    John Burkardt
!
!  Reference:
!
!    Timothy Sauer,
!    "How search engines rate page quality",
!    Numerical Analysis,
!    Pearson, 2006.
!    ISBN: 0-321-2698-9,
!    LC: QA297.S348
!
!  Output:
!
!    integer A(15,15): an adjacency matrix.
!
  implicit none

  integer, parameter :: node_num = 15

  integer A(node_num,node_num)

  A = reshape ( (/ &
     0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0, 0,  &
     0, 0, 1, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0,  &
     0, 1, 0, 0, 0, 1, 0, 1, 0, 0, 0, 0, 0, 0, 0,  &
     0, 0, 1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0,  &
     1, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 0,  &
     0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0,  &
     0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 0, 0,  &
     0, 0, 0, 1, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0,  &
     0, 0, 0, 0, 1, 1, 0, 0, 0, 1, 0, 0, 0, 0, 0,  &
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0,  &
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1,  &
     0, 0, 0, 0, 0, 0, 1, 1, 0, 0, 1, 0, 0, 0, 0,  &
     0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 0, 0, 0, 1, 0,  &
     0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 1, 0, 1, 0, 1,  &
     0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 1, 0, 1, 0/), (/ node_num, node_num /) )

  A = transpose ( A )

  return
end
subroutine digraph_adj_example_sixty ( A )

!*****************************************************************************80
!
!! digraph_adj_example_sixty() sets the adjacency matrix for the sixty digraph.
!
!  Discussion:
!
!    The nodes of the digraph are divisors of 60.  There is a link from I to
!    J if divisor I can be divided by divisor J.
!
!  Licensing:
!
!    This code is distributed under the MIT license. 
!
!  Modified:
!
!    11 August 2000
!
!  Author:
!
!    John Burkardt
!
!  Output:
!
!    integer A(node_num,node_num), the adjacency information.
!    A(I,J) is 1 if there is a direct link from node I to node J.
!
  implicit none

  integer, parameter :: node_num = 12

  integer A(node_num,node_num)
  integer d(node_num)
  integer i
  integer j

  d(1:12) = (/ 60, 30, 20, 15, 12, 10, 6, 5, 4, 3, 2, 1 /)

  do i = 1, node_num
    do j = 1, node_num
      if ( i == j ) then
        A(i,j) = 0
      else if ( mod ( d(i), d(j) ) == 0 ) then
        A(i,j) = 1
      else
        A(i,j) = 0
      end if
    end do
  end do

  return
end