yi作3次多项式拟合,与原系数比较。如果作2或4次多项式拟合,结果如何?解:MATLAB代码如下:clearallx=[1,2,3,4,5,6,7,8];y=[-3,-9,-15,-15,-3,27,81,165]z=y+rand(1,8);xi=1:0.1:8;p1=polyfit(x,z,2);zi=polyval(p1,xi);subplot(1,3,1);plot(x,z,'bo',xi,zi,'k');title('二次');p2=polyfit(x,z,3);zi=polyval(p2,xi);subplot(1,3,2);plot(x,z,'bo',xi,zi,'k');title('三次');p3=polyfit(x,z,4);zi=polyval(p3,xi);subplot(1,3,3);plot(x,z,'bo',xi,zi,'k');title('四次');MATLAB运行结果如下:y=-3-9-15-15-327811655.4用最小二乘法求一形如的经验公式拟合表5.11中的数据。表5.11已知数据1234567815.320.527.436.649.165.687.87117.6解:把y=a两边取对数,得:那个线性最小二乘法拟合参数和b,可得参数a的拟合值求解的MATLAB代码如下:x=[1:8]';y=[15.320.527.436.649.165.687.87117.6]';r=[ones(8,1),x];ab=r\log(y);ab(1)=exp(ab(1))x0=1:0.1:8;y0=ab(1).*exp(ab(2).*x0);plot(x,y,'o',x0,y0,'r')运算结果如下:ab=11.43580.2913求得的经验公式为:。----------THEEND,THEREISNOTXTFOLLOWING.------------
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