How to compute Cost function for linear regression
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Hi,
I am trying to compute cost function
I am using the following code:
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.
h = X * theta;
sError = (h - y) .^ 2;
J = sum(sError) / (2 * m);
% =========================================================================
end
.But I am getting the following error
Error in computeCost (line 7)
m = length(y); % number of training examples
.Please help
댓글 수: 6
답변 (10개)
João Marlon Souto Ferraz
2020년 9월 14일
I believe than this is happen because you are running and trying to compile the function. Just save and to call than function from the other script.
댓글 수: 0
Sanskar Choudhary
2021년 12월 28일
open file submit.m and then run it.(don't run computeCost.m file, this will not work because its just function)
댓글 수: 3
Abdulwaliyi
2022년 12월 12일
this is a nice answer
just use submit() then generate your token and run your answer
Prasad Kute
2021년 7월 23일
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.
J = (1/(2*m))*sum(((X*theta) - y).^2)
Try this, you will get it correct.
댓글 수: 2
Image Analyst
2022년 2월 4일
You say "sorry...I forgot to mention...I just hit run to execute the program and I get this error message.."
Well that is the whole problem. When you have a function that expects inputs like X, y, theta then you need to supply those inputs. You can't just click the green run triangle and expect somehow that doing that will automagically invent values for X, y, and theta. So you need to do something like
% Declare inputs:
X = rand(1,10);
y = rand(1, 10);
theta = 42;
% Now run the function:
result = computeCost(X, y, theta)
fprintf('Done with the program!\n');
%==========================================================================================
% Define the function:
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.
h = X * theta;
sError = (h - y) .^ 2;
J = sum(sError) / (2 * m);
end
댓글 수: 0
Image Analyst
2022년 2월 6일
As long as y is defined (like you assigned something to y before you called the function) then that line
m = length(y); % number of training examples
should work. However you didn't give the entire error message. You gave the line the error occurred on but not the actual error description. Why not? You need to include all the red text, not just some of it.
By the way you need to assign something for y, you can't just click the green Run triangle on the toolbar without assigning all the input variables.
댓글 수: 0
Jia He
2022년 2월 6일
If you meet errors in submitting, and your function is correct. Try to delete its .mlx file and submit it again.
댓글 수: 0
MAZEN ALHARBI
2022년 4월 5일
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
% number of training examples
% You need to return the following variables correctly
data = load('ex1data1.txt'); % read comma separated data
y = data(:, 2);
m = length(y); % number of training examples
X = [ones(m, 1), data(:,1)]; % Add a column of ones to x
theta = zeros(2, 1);
% ====================== YOUR CODE HERE ======================
% Instructions: Compute the cost of a particular choice of theta
% You should set J to the cost.
J = 0;
J = 1/(2*m) * (X * theta - y)' * (X * theta - y); % vectorized form
% =========================================================================
end
댓글 수: 1
safwan bin amir
2022년 4월 10일
@MAZEN ALHARBI you a life saviour. you are doing that ML course of andrew ng?
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