% Plot Data 散点图：程序实现绘制一个一X，y为数据，红色的x作为标记的散点图，标记大小为10，并加入横纵坐标轴的题目

plot(X, y, 'rx', 'MarkerSize', 10); % Plot the data

ylabel('Profit in $10,000s'); % Set the y?axis label

xlabel('Population of City in 10,000s'); % Set the x?axis label

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% Surface plot 表面图：程序以theta0_vals、theta1_vals为两个变量，J_vals为结果绘制表面图。注：theta0_vals、theta1_vals各为1*100的行向量，J_vals为100*100的方阵

figure;

surf(theta0_vals, theta1_vals,J_vals)

xlabel('\theta_0'); ylabel('\theta_1');

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% Contour plot 轮廓图，contour(x,y,z,v):其中x，y为横纵坐标，z为等高线值的大小，同样x为100*1，y为100*1，z为100*100;同时v向量规定了等高线的范围为（通过logspace函数取到10^-2 → 10^3，取20个值）

figure;

% Plot J_vals as 15contours spaced logarithmically between 0.01 and 100

contour(theta0_vals,theta1_vals, J_vals, logspace(-2, 3, 20))

xlabel('\theta_0'); ylabel('\theta_1');

hold on;

plot(theta(1), theta(2), 'rx', 'MarkerSize', 10, 'LineWidth', 2);

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