! 2.13.f90
! $Id: 2.13.f90 1.1 2014/02/15 09:05:33 s Exp $
!
program ex2_13

implicit none
integer :: i
real(8) :: c,eps,irr,left,mid,right

i=1
eps  =1.0e-3
left =0.0
right=1.0
mid=(left+right)/2.0

do while(abs(f(mid))>eps)
  if(f(mid)>0.0) then
    right=mid
  else
    left=mid
  end if
  mid=(left+right)/2.0
  i=i+1
end do

c=mid
irr=1.0/c-1.0

write(*,*) 'c= ',    c
write(*,*) 'f(c)= ', f(c)
write(*,*) 'i= ',    i

stop

contains

function f(c)
  implicit none
  real(8) :: f
  real(8) :: c,x(0:5)

  x(0)= -50.0
  x(1)=  12.0
  x(2)=  12.0
  x(3)=  12.0
  x(4)=  12.0
  x(5)=  12.0

  f=x(0) +x(1)*c +x(2)*c**2 +x(3)*c**3 +x(4)*c**4 +x(5)*c**5
  return
end function f


end program ex2_13
! end