说明：  利用解析的方法进行扇形束CT投影数据仿真，在内置函数fanbeam的基础上又增加了其他参数的设置，例如探测器的间距等。
(The fan-beam CT projection data are simulated by analytic method. On the basis of the built-in function fanbeam, other parameters are added, such as the spacing of detectors.)