!**************************************************************
!*     One-dimensional cellular automata with rule that       *
!*           generates a Sierpinski triangle                  *
!* ---------------------------------------------------------- *
!* Ref.: "Problem Solving with Fortran 90 By David R. Brooks, *
!*        Springer-Verlag New York, 1997".                    *
!************************************************************** 
Program Sierpinski

Implicit None  !All variables must be declared

Integer, parameter :: Size = 60

Logical a(Size), old_a(Size), a_1, a0, a1

Character*1 b(Size)

Integer i, j, cycle, n_cycles

Data n_cycles,a,b /15,Size*.FALSE.,Size*' '/

  cycle = 0
  a(Size/2) = .TRUE.  !start with a single live cell
  b(Size/2) = '*'
  
  print *,' '
  print *,'                                Sierpinski  Triangle'
  print *,' '
  Write(*,1000) cycle, b 

! Generate more cycles.

  Do i = 1, n_cycles
    old_a = a
    Do j = 2, Size-1
      a_1 = old_a(j-1)
      a0 = old_a(j)
      a1 = old_a(j+1)
      a(j) = (a_1.and.(.not.a0).and.(.not.a1))  &
	    .or.((.not.a_1).and.a1)
    End Do
    Do j = 1, Size
      If (a(j)) Then
        b(j) = '*'
      Else
        b(j) = ' '
      End If
    End Do
    Write(*,1000) i, b
  End Do

  print *,' '

1000 Format(' Generation ',i2,60a1)

End

!end of file sierpins.f90