clear all; clc; p=[0 500 2000 5000]; q=[1e-5 1.15e-5 1.8e-5 4.0e-5]; x_1=0:5000; a(:,1)=x_1; k1=interp1(p,q,abs(x_1),'linear'); a(:,2)=k1; [m,n]=find(a(:,1)==300|a(:,1)==1500|a(:,1)==3000); a1=a(m,2); subplot(3,1,1); plot(x_1,k1); title('一维线性插值'); x_2=0:5000; Lagrange(p,q,x_2); L=Lagrange(p,q,x_2); b=[L(301),L(1501),L(3001)]; y0=1:5000; yy=Zuixiao(p,q,y0); c=[yy(1,300),yy(1,1500),yy(1,3000)]; % *** 拉格朗日插值 *** function L = Lagrange(x,y,x_2) L = zeros(1,length(x_2)); for i = 1:1:length(x_2) l = ones(1,length(x)); for k = 1:1:length(x) for j= 1:1:length(x) if j ~= k l(k) = l(k) * ( x_2(i)-x(j)) / (x(k)-x(j)); end end L(i) = L(i) + l(k)*y(k); end end if nargout == 0 subplot(3,1,2); plot(x_2,L); title('拉格朗日插值'); end end % *** 最小二乘法 *** function yy=Zuixiao(x,y,y0) R(:,1)=x.^2; R(:,2)=x; R(:,3)=[1 1 1 1]; Y=y'; a=(R'*R)^-1*R'*Y; yy=a(1).*(y0.*y0)+a(2).*y0+a(3); subplot(3,1,3); plot(y0,yy); title('最小二乘法'); end我应该如何修改这段代码才能让三条曲线画在同一个图中

你可以将三条曲线的绘制放在同一个 subplot 中，具体修改如下：

clear all; clc; 
p=[0 500 2000 5000];
q=[1e-5 1.15e-5 1.8e-5 4.0e-5];
x_1=0:5000;
a(:,1)=x_1;
k1=interp1(p,q,abs(x_1),'linear');
a(:,2)=k1;
[m,n]=find(a(:,1)==300|a(:,1)==1500|a(:,1)==3000);
a1=a(m,2);

x_2=0:5000;
L=Lagrange(p,q,x_2);
b=[L(301),L(1501),L(3001)];

yy=Zuixiao(p,q,x_2);
c=[yy(1,300),yy(1,1500),yy(1,3000)];

subplot(1,3,1:3); % 修改subplot
plot(x_1,k1);
hold on; % 添加hold on
plot(x_2,L);
plot(x_2,yy);
legend('一维线性插值','拉格朗日插值','最小二乘法'); % 添加图例
title('插值方法比较');

% *** 拉格朗日插值 ***
function L = Lagrange(x,y,x_2)
    L = zeros(1,length(x_2));
    for i = 1:1:length(x_2)
        l = ones(1,length(x));
        for k = 1:1:length(x)
            for j= 1:1:length(x)
                if j ~= k
                    l(k) = l(k) * ( x_2(i)-x(j)) / (x(k)-x(j));
                end
            end
            L(i) = L(i) + l(k)*y(k);
        end
    end
end

% *** 最小二乘法 ***
function yy=Zuixiao(x,y,y0)
    R(:,1)=x.^2;
    R(:,2)=x;
    R(:,3)=[1 1 1 1];
    Y=y';
    a=(R'*R)^-1*R'*Y;
    yy=a(1).*(y0.*y0)+a(2).*y0+a(3);
end

修改后的代码会将三条曲线画在同一个图中，且添加了图例说明。