matlab - Matlab错误使用错误-矩阵尺寸必须一致

Question

我正在尝试编写用于数据分类的代码。我尝试实现一个sigmoid函数，然后尝试使用该函数来计算成本。我不断收到错误，我感觉是因为存在sigmoid函数。我希望sigmoid函数返回一个 vector 。它不断返回标量。

function g = sigmoid(z)
%SIGMOID Compute sigmoid functoon
%   J = SIGMOID(z) computes the sigmoid of z.

% You need to return the following variables correctly 

g=zeros(size(z));
m=ones(size(z));
% ====================== YOUR CODE HERE ======================
% Instructions: Compute the sigmoid of each value of z (z can be a matrix,
%               vector or scalar).


g=1/(m+exp(-z));

这是我的成本函数:

m = length(y); % number of training examples

% You need to return the following variables correctly 
grad=(1/m)*((X*(sigmoid(X*theta)-y)));//this is the derivative in gradient descent
J=(1/m)*(-(transpose(y)*log(sigmoid((X*theta))))-(transpose(1-y)*log(sigmoid((X*theta)))));//this is the cost function

X的尺寸为100,4； theta的值为4,1; y为100,1。

谢谢。

错误:

Program paused. Press enter to continue.

 sigmoid answer: 0.500000Error using  - 
Matrix dimensions must agree.

Error in costFunction (line 11)
grad=(1/m)*((X*(sigmoid(X*theta)-y)));

Error in ex2 (line 69)
[cost, grad] = costFunction(initial_theta, X, y);

Answer 1

请在方法sigmoid中将g=1/(m+exp(-z));替换为g=1./(m+exp(-z));

z = [2,3,4;5,6,7] ;
%SIGMOID Compute sigmoid functoon
%   J = SIGMOID(z) computes the sigmoid of z.

% You need to return the following variables correctly 

g=zeros(size(z));
m=ones(size(z));
% ====================== YOUR CODE HERE ======================
% Instructions: Compute the sigmoid of each value of z (z can be a matrix,
%               vector or scalar).


g=1./(m+exp(-z));