$$W(x)=\{\begin{array}{ll}\frac{1.}{2.}\{1.+\mathrm{余弦}(\frac{2.\pi }{R}[x-R/2.])\},\hfill & 0\le x<\frac{R}{2.}\hfill \\ 1.,\hfill & \frac{R}{2.}\le x<1.-\frac{R}{2.}\hfill \\ \frac{1.}{2.}\{1.+\mathrm{余弦}(\frac{2.\pi }{R}[x-1.+R/2.])\},\hfill & 1.-\frac{R}{2.}\le x\le 1.\hfill \end{array}$$