How to compute Cost function for linear regression

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

[infinity]

Hello,

in your code, what is "thetha" in

diff=thetha'*X - y;

[Muhammad Kundi]

thanks...sorry..it was typo mistake...I fixed it...its "theta" and not "thetha"...but still code not running

[infinity]

The error tell us that

Error in computeCostMulti (line 7)

but you show the function name

computeCost

they are not fit. Do you have the function "computeCostMulti"

[Muhammad Kundi]

Thanks for your kind help...Sorry ..actually...I pasted the code in the file with different name..i.e computeCostMulti....now I fixed it..its the same code...and the error message is ..

Error in computeCost (line 7)
m = length(y); % number of training examples

[Muhammad Kundi]

sorry...I forgot to mention...I just hit run to execute the program and I get this error message..

Do I have to run the function by inserting the values of x,y and theta???

[David Onoja]

Pls how do you submit answers

Answer 1

[João Marlon Souto Ferraz]

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.

Answer 2

[Mahdi Badriyan]

hi

J = sum(sError) / (2 .* m);

in this way your code will be corrected.

[Arunodhaya]

Hello

Answer 3

[Sanskar Choudhary]

open file submit.m and then run it.(don't run computeCost.m file, this will not work because its just function)

[Chinedu Adiegwu]

I don't understand, could you rephrase?

[David Onoja]

Pls explain better

[Abdulwaliyi]

this is a nice answer

just use submit() then generate your token and run your answer

Answer 4

[Ghayyur Abbas]

initialize x y theta with values in the function

[Nagesh Rathod]

how

[Tushant Verma]

computeCost(X,y,theta)

Answer 5

[Heng Dao]

((h)-y).^2 Try try hope can help u

Answer 6

[Prasad Kute]

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.

[amenallah berrejeb]

it doesn't work

[Image Analyst]

@amenallah berrejeb Why not? Show your code that proves it does not work.

Answer 7

[Image Analyst]

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

Answer 8

[Image Analyst]

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.

Answer 9

[Jia He]

If you meet errors in submitting, and your function is correct. Try to delete its .mlx file and submit it again.

Answer 10

[MAZEN ALHARBI]

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

[safwan bin amir]

@MAZEN ALHARBI you a life saviour. you are doing that ML course of andrew ng?