【原】Andrew Ng斯坦福机器学习（5）——Week2 Programming Quiz—实现
plotData
compute costfunction
1 function J = computeCost(X, y, theta) 2 %COMPUTECOST Compute cost for linear regression 3 % J = COMPUTECOST(X, y, theta) computes the cost of using theta as the 4 % parameter for linear regression to fit the data points in X and y 5 6 % Initialize some useful values 7 m = length(y); % number of training examples 8 9 % You need to return the following variables correctly 10 J = 0; 11 12 % ====================== YOUR CODE HERE ====================== 13 % Instructions: Compute the cost of a particular choice of theta 14 % You should set J to the cost. 15 16 % y is the class labels 17 18 m = size(X, 1); % number of training examples, size of rows 19 predictions = X * theta; % predictions of hapothesis on all m examples 20 sqrErrors = (predictions - y) .^ 2; % squared errors .^ 指的是对数据中每个元素平方 21 22 J = 1 / (2 * m) * sum(sqrErrors); 23 24 %disp(sprintf("computeCost %0.2f \n", J)); 25 % ========================================================================= 26 27 end
