	E_x	E_n	H_e
g₁	E_x₁ = 0	E_n₁ = (E_x₂ − E_x₁)/6	q
g₂	E_x₂ = (a + b)/2	E_n₂ = (E_x₂ − E_x₁)/6	q
g₃	E_x₃ = (b + c)/2	E_n₃ = (E_x₃ − E_x₂)/6	q
g₄	E_x₄ = d	E_n₄ = (Ex₄ − E_x₃)/6	q