! integrate_plain.f90 -- ! ! Example belonging to "Modern Fortran in Practice" by Arjen Markus ! ! This work is licensed under the Creative Commons Attribution 3.0 Unported License. ! To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0/ ! or send a letter to: ! Creative Commons, 444 Castro Street, Suite 900, Mountain View, California, 94041, USA. ! ! Test the code for the interface design problem - integration ! routines ! module integration_library implicit none contains subroutine integrate_trapezoid( f, xmin, xmax, steps, result ) interface real function f( x ) real, intent(in) :: x end function f end interface real, intent(in) :: xmin, xmax integer, intent(in) :: steps real, intent(out) :: result integer :: i real :: x real :: deltx if ( steps <= 0 ) then result = 0.0 return endif deltx = (xmax - xmin) / steps result = ( f(xmin) + f(xmax) )/ 2.0 do i = 2,steps x = xmin + (i - 1) * deltx result = result + f(x) enddo result = result * deltx end subroutine integrate_trapezoid end module integration_library module functions implicit none contains real function f( x ) real, intent(in) :: x f = x end function f end module functions program test_integrate use integration_library use functions implicit none real :: xmin, xmax, result integer :: steps xmin = 1.0 xmax = 10.0 steps = 10 call integrate_trapezoid( f, xmin, xmax, steps, result ) write(*,*) 'Computed: ', result write(*,*) 'Expected: ', 0.5*(xmin+xmax)*(xmax-xmin) end program test_integrate