A new method is presented to determine the fitting direction while using Dr. Bridge's linear editor to model various parabolas in this paper. By considering convex-concave property at monotone interval, parabolas' different shapes are determined. Based on the method, two set of symbols are introduced to describe the monotonicity and convex-concave property of parabola, and the judgment of parabola fitting type is determined. With the presented method, a quadratic parabola can be fitted by means of two controlling points as well as three controlling points. The method is illustrated by its simplicity and convenience, but efficient to program realization.
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