Numerical Methods yi + 1 = y_i + Phi (x_i, y_i, h) Consider the equation given above. The function phi (x, y, h) is an incremental function. It can be interpreted as the average of the slope at the initial and end points. a function of the initial x value only. an incremental function. It can be interpreted as the slope at the mid-point. an incremental function. It can be interpreted as a representative slope over the interval. Solution Option D.