initialize_integration_class Subroutine

    subroutine initialize_integration_class(me,fx,&
                                            xl,xu,tolx,methodx)

    implicit none

    class(integration_class_1d),intent(inout) :: me
    procedure(func_1d)    :: fx       !! 1d function: f(x)
    real(wp),intent(in)   :: xl       !! x integration lower bound
    real(wp),intent(in)   :: xu       !! x integration upper bound
    real(wp),intent(in)   :: tolx     !! error tolerance for dx integration
    integer,intent(in)    :: methodx  !! quadrature method to use for x

    ! select quadrature rule
    select case (methodx)
    case(6);  me%g => g6
    case(8);  me%g => g8
    case(10); me%g => g10
    case(12); me%g => g12
    case(14); me%g => g14
    case default
        error stop 'invalid quadrature method in initialize_integration_class'
    end select

    me%fun  => fx       !the function f(x) to integrate
    me%tol  = tolx      !tolerance
    me%a    = xl        !lower bound
    me%b    = xu        !upper bound

    end subroutine initialize_integration_class