Fortran实现二分法.txt

program main
      implicit none


      real, parameter :: epsilon=1e-6
      real :: xa,xb,xc,a
      real,external  ::  f

      a=1.0
      do while(a>0)
      write(*,*) "it is the first time or f(xa)*f(xb)>0"
      write(*,*) "please input proper xa and xb"

      read(*,*) xa,xb
      write(*,*) f(xa),f(xb)
      if(f(xa)*f(xb)<=0) exit
      end do

      do while  (xb-xa>epsilon)
      xc=(xa+xb)/2
    if (f(xa)*f(xc)<0) then
      xb=xc
      else
              xa=xc
      end if
      end do

      xc=(xa+xb)/2
      write(*,*) "the solution is:",xc
      end