Program test1
 implicit none

 real::  maximum, step
 integer:: i, n
 real :: Q, f
 real, external :: hamso

 Print *,"gia tri toi da cua truc x ?"
 read *,maximum
 Print *, "buoc nhay? "
 read *,step

 n = (maximum/step) -1

 Do i=1, n
  If (Q == 1.0) then
  goto 10
   end if
  f = hamso(Q)
 Open (1, file = 'point.doc')
 write (1) Q, f
  Print *, "ngang = ",Q, "Tung = ", f
10 Q = Q + step
 enddo

read *, maximum

End program test1

Function hamso(Q)
 implicit none
 real, intent(in):: Q
 real:: hamso

 hamso = (1.0/2.0) * sqrt((1.0-2.0*Q+ Q*Q)/(1.0-2.0*Q+2.0*Q * 0.8+Q*Q))   +1.0/2.0

end function hamso