function nusselt_correlation_der_Re(me,Re,Pra,Tother,T)
class(nusselt_t), intent(inout) :: me
real(dp), intent(in) :: Re,Pra
real(dp), intent(in), optional :: Tother,T
real(dp) :: nusselt_correlation_der_Re,Tother_loc,T_loc
real(dp) :: eps
if(present(Tother) .and. present(T)) then
Tother_loc=Tother; T_loc=T
else
Tother_loc=0.0_dp; T_loc=0.0_dp
endif
if(associated(me%nuss_der_Re)) then
nusselt_correlation_der_Re=me%nuss_der_Re(me%nuss_cfg,Re,Pra,Tother_loc,T_loc)
else
eps=2.0e-1_dp
if(Re >= 0.5_dp*eps) then
nusselt_correlation_der_Re=(me%nuss(me%nuss_cfg,Re+0.5_dp*eps,Pra,Tother_loc,T_loc) &
-me%nuss(me%nuss_cfg,Re-0.5_dp*eps,Pra,Tother_loc,T_loc))/eps
else
nusselt_correlation_der_Re=(me%nuss(me%nuss_cfg,Re+eps,Pra,Tother_loc,T_loc) &
-me%nuss(me%nuss_cfg,Re,Pra,Tother_loc,T_loc))/eps
endif
endif
end function nusselt_correlation_der_Re