各位大侠请帮助小弟:怎样用一个周期的正弦函数去拟合下面这81个点（跪求啊）

[shitounaodai]

y=[28.9 29.5 29.6 30.2 31.4 31.6 31.6 32.1 32.0 32.05 32.0 32.0 32.0 32.0 31.8 31.3 31.2 31 30.8 30.7 30.3 30 29.2 28.4 28.0 27.5 27 26.9 26.2 26.0 25.8 25.0 24.7 24.2 24.0 23.2 22.8 22.7 22.2 22.7 22.8 22.6 22.7 22.3 22.2 22.4 22.0 22.0 22.7 23.2 23.1 23.1 23 23.2 22.9 23.3 22.7 23.3 22.0 22.0 22.0 21.8 21.9 22.1 22.5 22.7 23.5 23.8 24.2 24.3 24.1 24.9 25.3 25.8 26.2 26.5 27.2 27.4 27.8 28.2 28.7 ];
跪求代码:(:(

[slgu]

x=0:80;
y=[28.9, 29.5, 29.6, 30.2, 31.4, 31.6, 31.6, 32.1, 32.0, 32.05, 32.0, 32.0, 32.0, 32.0, 31.8, 31.3, 31.2, 31.0, 30.8, 30.7, 30.3, 30.0, 29.2, 28.4, 28.0, 27.5, 27.0, 26.9, 26.2, 26.0, 25.8, 25.0, 24.7, 24.2, 24.0, 23.2, 22.8, 22.7, 22.2, 22.7, 22.8, 22.6, 22.7, 22.3, 22.2, 22.4, 22.0, 22.0, 22.7, 23.2, 23.1, 23.1, 23.0, 23.2, 22.9, 23.3, 22.7, 23.3, 22.0, 22.0, 22.0, 21.8, 21.9, 22.1, 22.5, 22.7, 23.5, 23.8, 24.2, 24.3, 24.1, 24.9, 25.3, 25.8, 26.2, 26.5, 27.2, 27.4, 27.8, 28.2, 28.7]

fx=@(b,x)b(1)+b(2)*sin(b(3)*x.^b(4)+b(5));
b=[26.99407901, 5.179534879, 0.3051903923, 0.6883101874, 0.2039824941];
b=lsqcurvefit(fx,b,x,y)
b=nlinfit(x,y,fx,b)
y1=fx(b,x);
plot(x,y,'o',x,y1)