d_trapz2d_func_recursive Function

function d_trapz2d_func_recursive(func,xrange,yrange,N0,iterative,threshold) result(int)
  interface
     function func(x)
       real(8),dimension(:) :: x
       real(8)              :: func
     end function func
  end interface
  real(8),dimension(2)      :: xrange,yrange
  integer                   :: N,icount
  real(8)                   :: int,eps,int0
  integer,optional          :: N0
  integer                   :: N0_
  logical,optional          :: iterative
  logical                   :: iterative_
  real(8),optional          :: threshold
  real(8)                   :: threshold_
  iterative_=.false.;if(present(iterative))iterative_=iterative
  N0_=51;if(present(N0))N0_=N0
  threshold_=1d0;if(iterative_)threshold_=5.d-3
  if(present(threshold))threshold_=threshold
  N=N0_
  eps=1d0
  icount=1
  int=d_trapz2d_func(func,xrange,yrange,N,N)
  do while (eps>threshold_)
     icount=icount+1
     int0=int
     N=2*N-10
     int=d_trapz2d_func(func,xrange,yrange,N,N)
     eps=abs(int-int0)/abs(int)
  enddo
end function d_trapz2d_func_recursive