\magnification=\magstep2

$$
y_1 \quad = \quad y_i \ + \ k_1 \thinspace ( {{1}\over{2}} \thinspace dt )
$$

$$
y_2 \quad = \quad y_i \ + \ k_2 \thinspace ( {{1}\over{2}} \thinspace dt )
$$

$$
y_3 \quad = \quad y_i \ + \ k_3 \thinspace dt
$$

$$
y_{i+1} \quad = \quad y_i \ + \ {{1}\over{6}} 
                        ( k_1 + 2 k_2 + 2 k_3 + k_4 ) \thinspace dt
$$



\bye

