!Simpson method for integral

module INTEGRAL

implicit none

contains

real function integ(a,b,m)  !subfunction

implicit none

real a,b,l

integer m,i

real datas(m)

real,external::func

if(mod(m,2)==0) then

write(*,*) 'm is an even number,please enter an odd number'

end if

forall(i=1:m)  !build an array 

  datas(i)=a+(i-1)*l/(m-1)

end forall

l=b-a

integ=0

!!!!!!!!enter to the key code segment

integ=datas(1)+datas(m)

do i=2,m-1

if(mod(i,2)==0) then

  integ=integ+4.0*f(datas(i))

  else 

  integ=integ+2.0*f(datas(i))

end if

end do

integ=integ*l/(m-1)/3.0

return

end function

real function f(x) !the function to be solved

implicit none

real x

f=x+sin(x)

return

end function

end module

!!!!!!!!!!!!!!!!!!!!!!!!!!!!

!main progam

program main

use INTEGRAL

implicit none

real a,b     !a is the lower limit of integral 

             !b is the upper limit of integral

integer m    !m is the number of the dot to be given,and m must be a odd

write(*,*) 'please enter a'

read(*,*) a

write(*,*) 'please enter b (b>a)'

read(*,*) b

write(*,*) 'please enter m'

read(*,*) m

write(*,*) integ(a,b,m)

stop 

end