Matlab錯誤錯誤使用 - 矩陣尺寸必須一致

Question

我想寫一個代碼分類的數據。我嘗試實現一個sigmoid函數，然後嘗試在計算成本時使用該函數。我不斷收到錯誤，並且我有一種感覺，那是因爲sigmoid函數。我希望sigmoid函數返回一個vector.But它不斷返回一個標量。

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)); 

這是我的成本函數：

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的尺寸爲100,4; θ是4,1; y是100,1。

謝謝你。

錯誤：

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

請在你的方法乙狀結腸

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));