1、MATLAB:polyfit:XYSizeMismatch,. X and Y vectors must be the same size.)end%检验X Y维数是否匹配x = x(:);y = y(: if nargout 2 mu = mean(x); std(x); x = (x - mu(1)/mu(2);%利用范德蒙德矩阵构造方程组系数矩阵V(:,n+1) = ones(length(x),1,class(x);for j = n:-1:1 V(:,j) = x.*V(:,j+1);% 对矩阵进行QR分解以求得多项式系数值Q,R = qr(V,0);ws = warning(off
2、,allp = R(Q*y);warning(ws);if size(R,2) size(R,1) warning(PolyNotUnique, .Polynomial is not unique; degree = number of data points.elseif condest(R) 1.0e10 if nargout RepeatedPointsPolynomial is badly conditioned. Remove repeated data points. elseRepeatedPointsOrRescale Polynomial is badly condition
3、ed. Remove repeated data pointsn . or try centering and scaling as described in HELP POLYFIT.) endr = y - V*p;p = p.; % 将多项式系数默认为行向量.5、运行流程图 过程:clearx = 0.5000 1.0000 1.5000 2.0000 2.5000 3.0000y=1.75 2.45 3.81 4.80 8.00 8.60x1=0.5:0.05:3.0;p=mypolyfit(x,y,2)y1=p(3)+p(2)*x1+p(1)*x1.2;plot(x,y,*hold
4、onplot(x1,y1,r二、编程计算以下电路问题例8-1-3如图所示电路,已知R=5,L=3,=5,Uc=10,求R,C,和L,S,并画其相量图。理论分析:根据电路分析Z=R+j*(Xl-Xc)Ic=Uc/Z3;Z3=-j*XcIr=Ur/Z2=Uc/Z2;Z2=RI=Ir+IcUl=I*Z1;Z1=j*XLUs=Ul+Ur计算得Ir =2;Ic =2.00iI =2.00 + 2.00iUl =-6.00 + 6.00iUs =4.00 + 6.00iR=5;XL=3;XC=5;UC=10;UR=UC;%为给定元件赋值Z1=j*XL;Z2=R;Z3=-j*XC;%定义各电抗disp(电流
5、IR=UR/Z2%计算IRIC=UC/Z3%计算ICI=IR+IC%计算I电压UL=I*Z1%计算ULUS=UC+UL%计算USIR IC I UL US幅值disp(abs(IR,IC,I,UL,US)相角disp(angle(IR,IC,I,UL,US)*180/pi)ph=compass(IR,IC,I,UL,US);%分别画出IR,IC,I,UL,US相量图set(ph,linewidth,3)运行流程图:运行图三、编程解决以下问题求自然三次样条曲线,经过点(-3,2),(-2,0),(1,3),(4,1),而且自由边界条件(-3)=0,(4)=0。算法说明:三次样条也是分片三次插值函
6、数,它是在给定的区间a,b上的一个划分:a=x0x1=x0(j)&(x(k)x0(j+1) l(k)=j; sum=(3*(x0(l(k)+1)-x(k)2/h(l(k)2-2*(x0(l(k)+1)-x(k)3/h(l(k)3)*y0(l(k); sum=sum+(3*(x(k)-x0(l(k)2/h(l(k)2-2*(x(k)-x0(l(k)3/h(l(k)3)*y0(l(k)+1); sum=sum+h(l(k)*(x0(l(k)+1)-x(k)2/h(l(k)2-(x0(l(k)+1)-x(k)3/h(l(k)3)*m(l(k); s(k)=sum-h(l(k)*(x(k)-x0(l(k)2/h(l(k)2-(x(k)-x0(l(k)3/h(l(k)3)*m(l(k)+1);举例:x=-3 -2 1 4y=2 0 3 1x0=-3:0.15:4;y0=myspline(x,y,0,0,x0);plot(x0,y0)hold on orlegend(计算值实验值
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