MATLAB实现cost function计算和gradience descent计算

cost function计算：

function J = computeCost(X, y, theta)
%COMPUTECOST Compute cost for linear regression
%   J = COMPUTECOST(X, y, theta) computes the cost of using theta as the
%   parameter for linear regression to fit the data points in X and y

% Initialize some useful values
m = length(y); % number of training examples

% You need to return the following variables correctly 
J = 0;

% ====================== YOUR CODE HERE ======================
% Instructions: Compute the cost of a particular choice of theta
%               You should set J to the cost.
<span style="color:#cc0000;"><strong>h=X*theta;
sError=(h-y).^2;%注意点之前有空格 表示每个元素取平方 如果不加点则表示矩阵的平方
J=sum(sError)/(2*m);</strong></span>




% =========================================================================

end