请教各位大侠一个matlab程序问题

flystardong

x = 0:0.01:20;
y1 = 200*exp(-0.05*x).*sin(x);
y2 = 0.8*exp(-0.5*x).*sin(10*x);
[AX,H1,H2] = plotyy(x,y1,x,y2,'plot');
set(H1,'color','red')

set(get(AX(2),'Ylabel'),'String','Fast Decay')
xlabel('Time (\musec)')

title('Multiple Decay Rates')
如上程序运行过程中，总是报错：
double
Attempt to call constructor double with incorrect letter case.
Error in linspace (line 20)
n = double(n);
Error in D:\Matlab\toolbox\matlab\graph2d\plotyy.p>plotyy (line 137)
Error in double (line 4)
[AX,H1,H2] = plotyy(x,y1,x,y2,'plot');
运行报错,但是出波形,如下:但是没有对坐标轴的标注以及图例的标注