Converts the first segment of the pwl cost to linear quadratic.
        FIXME: Curve-fit for all segments.

def pwl_to_poly(self):
        """ Converts the first segment of the pwl cost to linear quadratic.
        FIXME: Curve-fit for all segments.
        """
        if self.pcost_model == PW_LINEAR:
            x0 = self.p_cost[0][0]
            y0 = self.p_cost[0][1]
            x1 = self.p_cost[1][0]
            y1 = self.p_cost[1][1]
            m = (y1 - y0) / (x1 - x0)
            c = y0 - m * x0

            self.pcost_model = POLYNOMIAL
            self.p_cost = (m, c)
        else:
            return