实验四插值和拟合
,-0.8090,-0.9511,-1.0000,-0.9511,-0.8090,-0.5878,-0.3090,-0.0000]; y2=polyfit(x,y,2);z2=polyval(y2,x); y3=polyfit(x,y,3);z3=polyval(y3,x); y4=polyfit(x,y,4);z4=polyval(y4,x); y5=polyfit(x,y,5);z5=polyval(y5,x);
plot(x,y,'k+',x,z2,'r*',x,z3,'g:',x,z4,'b-',x,z5,'y.')
3 已知x=[0.1,0.8,1.3,1.9,2.5,3.1],y=[1.2,1.6,2.7,2.0,1.3,0.5],用不同的方法求x=2点的插值,并分析所得结果有何不同.
x0=[0.1,0.8,1.3,1.9,2.5,3.1]; y0=[1.2,1.6,2.7,2.0,1.3,0.5]; yi0=interp1(x0,y0,2,'nearest') yi1=interp1(x0,y0,2,'spline') yi2=interp1(x0,y0,2,'linear') 4 已知热敏电阻数据
温度t(0C) 20.5 32.7 51.0 73.0 95.7 电阻R(?) 765 826 873 942 1032 求60C时的电阻R。（用拟合方法） t=[20.5,32.7,51.0,73.0,95.7]; r=[765,826,873,942,1032]; A=polyfit(t,r,2); r=polyval(A,60) 5 对函数f(x)?1，x?[-5,5]，分别用分段线性插值和三次样条插值作插值（其中插值节点1?x2不少于20），并分别作出每种插值方法的误差曲线.
x0=[-5,-4.5,-4,-3.5,-3,-2.5,-2,-1.5,-1,-0.5,0,0.5,1,1.5,2,2.5,3,3.5,4,4.5,5];
y0=[0.0385,0.0471,0.0588,0.0755,0.1000,0.1379,0.2000,0.3077,0.5000,0.8000,1.0000,0.8000,
0.5000,0.3077,0.2000,0.1379,0.1000,0.0755,0.0588,0.0471,0.0385];
x=-5:0.5:5;y=interp1(x0,y0,x,'spline');subplot(1,2,1);plot(x0,y0,'m+',x,y,'g'); x=-5:0.5:5;y=interp1(x0,y0,x,'linear');subplot(1,2,2);plot(x0,y0,'k+',x,y,'r')
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