-(a(x)u'(x))' = f(x) for all x belongs to I = (0,1) a(x)u'(0) = k_0(u(0) - g_0) -a(x)u'(1) = k_1(u(1) - g_1) Which is Robin general boundry condition (BC). If k_i = 0, this implies Neumann BC (in the ...