figure大小的设定：

大小的参数由units来控制，有normalized, inches, centimeters, points, characters，默认是characters，所以设置width和height为160,50时，界面大小看起来和正方形差不多，因为

characters是以系统默认的字符宽长为基准的。

修改为pixels，以屏幕像素为基准：

normalized — Units map the lower-leftcorner of the figure window to (0,0) and the upper-right corner to (1.0,1.0).

inches, centimeters, and points — Absoluteunits. 1 point = 1/72 inch.

pixels — Size depends on screen resolution.

characters — Based on the size ofcharacters in the default system font. The width of one characters unit is thewidth of the letter x, and the height of one characters unit is the distancebetween the baselines of two lines of text.