program trapezoid

	! integrate sin(x) over the interval 0 to pi
	! using trapezoid rule
	implicit none
	integer :: i, n = 11, nm
	real :: pi, f1, f2, x1, x2, xint

	write(*, "('  i        x       f(x)    int(f(x))'/&

          &'  1      0.00      1.00      0.00' )" )
	pi = acos(-1.0)
	nm = n-1
	xint = 0.0
	x1 = 0.0
	do i = 2, n
		x2 = ((i-1)/nm)*pi
		f1 = cos(x1)
		f2 = cos(x2)
		xint = xint + 0.5*(f1+f2)*(x2-x1)
		x1 = x2
		write(*, '(i3, 3(f10.2))') i, x2, f2, xint
	enddo
end program trapezoid