program integ
 use fvn
 implicit none
 real(8), external :: f1,f2,g,h
 real(8) :: a,b,epsabs,epsrel,abserr,res
 integer :: key,ier
 a=0.
 b=1.
 epsabs=1d-8
 epsrel=1d-8
 key=2
 call fvn_integ_1_gk(f1,a,b,epsabs,epsrel,key,res,abserr,ier)
 write(*,*) "Integration of x*x between 0 and 1 : "
 write(*,*) res
 call fvn_integ_2_gk(f2,a,b,g,h,epsabs,epsrel,key,res,abserr,ier)
 write(*,*) "Integration of x*y between 0 and 1 on both x and y : "
 write(*,*) res

end program
function f1(x)
 implicit none
    real(8) :: x,f1
    f1=x*x
end function
function f2(x,y)
 implicit none
    real(8) :: x,y,f2
    f2=x*y
end function
function g(x)
 implicit none
    real(8) :: x,g
    g=0.
end function
function h(x)
 implicit none
    real(8) :: x,h
    h=1.
end function