PROGRAM trap1 ! ! Author: Br. David Carlson ! ! Date: January 1, 2000 ! ! Revised: April 22, 2004; April 18, 2016 ! ! This program finds the approximate value of the integral of ln(x+1) from 1/4 to 3/4. ! The trapezoidal rule is used. IMPLICIT NONE INTEGER, PARAMETER::num = 100 ! Number of strips of area to sum up. REAL::a, b, pi, delta, sum, area, x INTEGER::k ! Function used: REAL::f WRITE (*, *) 'Program to integrate ln(x+1) from 1/4 to 3/4.' a = 0.25 b = 0.75 delta = (b - a) / num x = a + delta ! Note the a. sum = (f(a) + f(b)) / 2.0 DO k = 1, num - 1 sum = sum + f(x) x = x + delta END DO area = delta * sum WRITE (*, 100) area 100 FORMAT (1X, 'The trapezoidal rule gives an integral value of: ', E17.7) END PROGRAM ! Given: x a real value ! Task: Compute f(x) and return it. ! Return: Computed value in function name. REAL FUNCTION f(x) IMPLICIT NONE REAL, INTENT(IN)::x f = LOG(x + 1) END FUNCTION