# Coursera: Machine Learning (Week 2) [Assignment Solution] - Andrew NG

▸ Linear regression and get to see it work on data.

I have recently completed the Machine Learning course from Coursera by Andrew NG.

While doing the course we have to go through various quiz and assignments.

Here, I am sharing my solutions for the weekly assignments throughout the course.

These solutions are for reference only.

> It is recommended that you should solve the assignments by yourself honestly then only it makes sense to complete the course.
> But, In case you stuck in between, feel free to refer to the solutions provided by me.

#### NOTE:

Don't just copy paste the code for the sake of completion.
Even if you copy the code, make sure you understand the code first.

Since there is NO assignment in week-1, Let's start with the week-2 assignment....

In this exercise, you will implement linear regression and get to see it work on data. Before starting on this programming exercise, we strongly recommend watching the video lectures and completing the review questions for the associated topics.

It consist of the following files:
• ex1.m - Octave/MATLAB script that steps you through the exercise
• ex1 multi.m - Octave/MATLAB script for the later parts of the exercise
• ex1data1.txt - Dataset for linear regression with one variable
• ex1data2.txt - Dataset for linear regression with multiple variables
• submit.m - Submission script that sends your solutions to our servers
• Simple example function in Octave/MATLAB
• Function to display the dataset
• Function to compute the cost of linear regression
• Function to run gradient descent
• Cost function for multiple variables
• Gradient descent for multiple variables
• Function to normalize features
• Function to compute the normal equations
• YouTube videos featuring Free IOT/ML tutorials
* indicates files you will need to complete
# indicates optional exercises

### warmUpExercise.m :

```function A = warmUpExercise()
%WARMUPEXERCISE Example function in octave
%   A = WARMUPEXERCISE() is an example function that returns the 5x5 identity matrix

A = [];
% ============= YOUR CODE HERE ==============
% Instructions: Return the 5x5 identity matrix
%               In octave, we return values by defining which variables
%               represent the return values (at the top of the file)
%               and then set them accordingly.

A = eye(5);  %It's a built-in function to create identity matrix

% ===========================================
end```

### plotData.m :

```function plotData(x, y)
%PLOTDATA Plots the data points x and y into a new figure
%   PLOTDATA(x,y) plots the data points and gives the figure axes labels of
%   population and profit.

figure; % open a new figure window

% ====================== YOUR CODE HERE ======================
% Instructions: Plot the training data into a figure using the
%               "figure" and "plot" commands. Set the axes labels using
%               the "xlabel" and "ylabel" commands. Assume the
%               population and revenue data have been passed in
%               as the x and y arguments of this function.
%
% Hint: You can use the 'rx' option with plot to have the markers
%       appear as red crosses. Furthermore, you can make the
%       markers larger by using plot(..., 'rx', 'MarkerSize', 10);

plot(x, y, 'rx', 'MarkerSize', 10); % Plot the data
ylabel('Profit in \$10,000s'); % Set the y-axis label
xlabel('Population of City in 10,000s'); % Set the x-axis label

% ============================================================
end```

### computeCost.m :

```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.

%%%%%%%%%%%%% CORRECT %%%%%%%%%
% h = X*theta;
% temp = 0;
% for i=1:m
%   temp = temp + (h(i) - y(i))^2;
% end
% J = (1/(2*m)) * temp;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%% CORRECT: Vectorized Implementation %%%%%%%%%
J = (1/(2*m))*sum(((X*theta)-y).^2);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

% =========================================================================
end```

```function [theta, J_history] = gradientDescent(X, y, theta, alpha, num_iters)
%   taking num_iters gradient steps with learning rate alpha

% Initialize some useful values
m = length(y); % number of training examples
J_history = zeros(num_iters, 1);

for iter = 1:num_iters

% ====================== YOUR CODE HERE ======================
% Instructions: Perform a single gradient step on the parameter vector
%               theta.
%
% Hint: While debugging, it can be useful to print out the values
%       of the cost function (computeCost) and gradient here.
%

%%%%%%%%% CORRECT %%%%%%%
%error = (X * theta) - y;
%temp0 = theta(1) - ((alpha/m) * sum(error .* X(:,1)));
%temp1 = theta(2) - ((alpha/m) * sum(error .* X(:,2)));
%theta = [temp0; temp1];
%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%% CORRECT %%%%%%%
%error = (X * theta) - y;
%temp0 = theta(1) - ((alpha/m) * X(:,1)'*error);
%temp1 = theta(2) - ((alpha/m) * X(:,2)'*error);
%theta = [temp0; temp1];
%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%% CORRECT %%%%%%%
error = (X * theta) - y;
theta = theta - ((alpha/m) * X'*error);
%%%%%%%%%%%%%%%%%%%%%%%%%

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

% Save the cost J in every iteration
J_history(iter) = computeCost(X, y, theta);

end
end```

### computeCostMulti.m :

```function J = computeCostMulti(X, y, theta)
%COMPUTECOSTMULTI Compute cost for linear regression with multiple variables
%   J = COMPUTECOSTMULTI(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));

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

end```

```function [theta, J_history] = gradientDescentMulti(X, y, theta, alpha, num_iters)
%   taking num_iters gradient steps with learning rate alpha

% Initialize some useful values
m = length(y); % number of training examples
J_history = zeros(num_iters, 1);

for iter = 1:num_iters

% ====================== YOUR CODE HERE ======================
% Instructions: Perform a single gradient step on the parameter vector
%               theta.
%
% Hint: While debugging, it can be useful to print out the values
%       of the cost function (computeCostMulti) and gradient here.
%

%%%%%%%% CORRECT %%%%%%%%%%
error = (X * theta) - y;
theta = theta - ((alpha/m) * X'*error);
%%%%%%%%%%%%%%%%%%%%%%%%%%%

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

% Save the cost J in every iteration
J_history(iter) = computeCostMulti(X, y, theta);

end
end```

### featureNormalize.m :

```function [X_norm, mu, sigma] = featureNormalize(X)
%FEATURENORMALIZE Normalizes the features in X
%   FEATURENORMALIZE(X) returns a normalized version of X where
%   the mean value of each feature is 0 and the standard deviation
%   is 1. This is often a good preprocessing step to do when
%   working with learning algorithms.

% You need to set these values correctly
X_norm = X;
mu = zeros(1, size(X, 2));
sigma = zeros(1, size(X, 2));

% ====================== YOUR CODE HERE ======================
% Instructions: First, for each feature dimension, compute the mean
%               of the feature and subtract it from the dataset,
%               storing the mean value in mu. Next, compute the
%               standard deviation of each feature and divide
%               each feature by it's standard deviation, storing
%               the standard deviation in sigma.
%
%               Note that X is a matrix where each column is a
%               feature and each row is an example. You need
%               to perform the normalization separately for
%               each feature.
%
% Hint: You might find the 'mean' and 'std' functions useful.
%

mu = mean(X);
sigma = std(X);
X_norm = (X - mu)./sigma;

% ============================================================
end```

### normalEqn.m :

```function [theta] = normalEqn(X, y)
%NORMALEQN Computes the closed-form solution to linear regression
%   NORMALEQN(X,y) computes the closed-form solution to linear
%   regression using the normal equations.

theta = zeros(size(X, 2), 1);

% ====================== YOUR CODE HERE ======================
% Instructions: Complete the code to compute the closed form solution
%               to linear regression and put the result in theta.
%

% ---------------------- Sample Solution ----------------------

theta = pinv(X'*X)*X'*y;

% -------------------------------------------------------------
% ============================================================
end```

I tried to provide optimized solutions like vectorized implementation for each assignment. If you think that more optimization can be done, then put suggest the corrections / improvements.

--------------------------------------------------------------------------------
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Feel free to ask doubts in the comment section. I will try my best to solve it.
If you find this helpful by any mean like, comment and share the post.
This is the simplest way to encourage me to keep doing such work.

Thanks and Regards,
-Akshay P. Daga

### 155 تعليقات

1. Have you got prediction values as expected?

1. Yes. We got prediction values as expected.

2. My program was successfully run.But after hitting submit and giving the token this error is showing please help

ERROR--

% Total % Received % Xferd Average Speed Time Time Time Current
100 1115 100 25 100 1090 12 554 0:00:02 0:00:01 0:00:01 558
error: structure has no member 'message'
error: called from
submitWithConfiguration at line 35 column 5
submit at line 45 column 3
error: evaluating argument list element number 2
error: called from
submitWithConfiguration at line 35 column 5
submit at line 45 column 3
>>

3. Submitting configuration is generally related that your directory is not right! Or it could also mean you didn't extract the file properly...it did happen with me at times

4. I have similar problem please tell if you had solved it

2. Thanks for your comments. I still have some problems with the solutions, could you help me. In this case is with line 17, J History....

Week 2
function [theta, J_history] = gradientDescent(X, y, theta, alpha, num_iters)
% taking num_iters gradient steps with learning rate alpha

% Initialize some useful values

X = data(:,1)
y = data(:,2)
m = length(y)
x = [ones(m, 1), data(:,1)]
theta = zeros(2, 1)
iterations = 1500
alpha = 0.01
J = (1 / (2* m) ) * sum(((x* theta)-y).^2)
J_history = zeros(num_iters, 1)

for iter = 1:num_iters

% ====================== YOUR CODE HERE ======================
% Instructions: Perform a single gradient step on the parameter vector
% theta.
%
% Hint: While debugging, it can be useful to print out the values
% of the cost function (computeCost) and gradient here.
%

%error = (X * theta) - y;
%temp0 = theta(1) - ((alpha/m) * sum(error .* X(:,1)));
%temp1 = theta(2) - ((alpha/m) * sum(error .* X(:,2)));
%theta = [temp0; temp1];

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

% Save the cost J in every iteration
J_history(iter) = computeCost(X, y, theta);

end

end

1. change the variable name of iteration.num_iters must be same with declared variable named iteration

2. Can you elaborate?

3. Hi Can anyone help me. Just now i started ML. I am using Octave UI where i write the code but i don't know how to submit using UI. Can anybody please help me.

Watch this video by one of the mentors you will get it .

5. Thanks Hrishikesh, your comment might help many people.

error: 'y' undefined near line 7 column 12
error: called from
gradientDescent at line 7 column 3
>> computeCost()
error: 'y' undefined near line 7 column 12
error: called from
computeCost at line 7 column 3

How to correct this?

1. I tried to re-ran the code and everything worked perfectly fine with me.
In the code, you can variable "y" is defined in parameter list itself.
So, logically you should not get that error.
There must something else you might be missing outside these functions.

2. I used to get the same error! i realized i have to execute ex1.m file and ex1_multi.m files to correct our code.

3. Thank you for your response.
It will be helpful for many others...

4. Hey @Akshay...I am facing same problem of 'y' undefined.
I tried all the ways suggested by you and by others can you please help me out.
Can u please tell which version of octave should i use for windows 8.1 64 bit,presently I am using 4.4.1 may be due to that I am facing this problem,please help

4. computeCost

error: 'y' undefined near line 8 column 12
error: called from
computeCost at line 8 column 3

error: 'y' undefined near line 7 column 12
error: called from
gradientDescent at line 7 column 3

How to correct this?

1. I tried to re-ran the code and everything worked perfectly fine with me.
In the code, you can variable "y" is defined in parameter list itself.
So, logically you should not get that error.
There must something else you might be missing outside these functions.

If you got the solution please confirm here. It will be helpful for others.

2. Hi,
Receiving similar error. Found a solution?

3. Hello,
Got a similar error!
found the solution?

4. Hello,
Got a similar error!
found the solution?

5. Hi Sasank,
because small y already is used as a input argument for the mentioned functions. So, you can't get the error like y is undefined.
Are you sure you haven't made any mistake like small y and Capital Y ?
Please check it and try again.

6. error: 'X' undefined near line 9 column 10
error: called from
featureNormalize at line 9 column 8

7. anyone have find the solution? getting the same error from the program. i have try number of way but getting he same problem

8. yes i am also getting the same error

9. i have the solution : you have to load data x,y

>>X = data(:,1);
>>y = data(:,2);
>>m = length(y);
>>x=[ones(m,1),data(:,1)];
>>theta = zeros(2,1);
>>computeCost(X,y,theta)

if you have any question Pls contact me in my instagram name t.boy__jr

5. I was stuck for two months in Week 2 Assignment of Machine Learning . Thanx for your guidance due to which I can now understand coding in a better way and finally I have passed 2nd Week Assignment.

1. Glad to know that my work helped you in understanding the topic / coding.
You can also checkout free IOT tutorials with source codes and demo here: https://www.apdaga.com/search/label/IoT%20%28Internet%20of%20Things%29
Thanks.

6. I tried to reran the code. But i am getting error this:
error: 'num_iters' undefined near line 17 column 19
error: called from
gradientDescent at line 17 column 11
how to correct this??

1. i m also facing the same problem, plz help me to out of the problem

2. Facing the same problem...

7. i am also submitting these assignments . i have also done the same . But i dont know where to load data .thus my score is 0. how can i improve? please suggest me.

1. Refer the forum within the course in Coursera.

They have explained the step to submit the assignments in datails.

8. Hello ,

In the gradient descent.m file : theta = theta - ((alpha/m) * X'*error);
I m confused, why do we take the transpose of X (X'*error) instead
of X ?

B

1. Hi Bruno,
I got your confusion, Here X (capital X) represent all the training data together, each row as one training sample, each column as a feature. We want to multiply each training data with corresponding error. To make it happen you have to transpose of X (capital X).

if you take x (small x) as single training sample then you don't have to worry about transpose and all.
Simply (x * error) will work.

Try to do it manually on a notebook. You will understand it.

2. Hi Akshay

Thank you for the quick reply & help ...It s totally clear now, make sense !!!

Have a great day
Bruno

9. Good day,please am kind of stuck with week2 programming assignment,and this is under computecost.m
I already imported the data and plotted the scatter plot.Do I also after to import the data in computecost.m working area,and and when I just in inputted the code J = (1/(2*m))*(sum(((X*theta)-y).^2)); I got an error message.please how do I fix this.
Thanks

1. What error you got?

10. plotData

error: 'X' undefined near line 20 column 6
error: called from
plotData at at line 20 column 1

What is the solution to this?

1. Hi Amit, As I checked I have used small x as an input argument for plotData function.
and in your error there is capital X.
Are you sure you haven't made mistake in small and capital X?
Please check and try once again.

2. i can see you have used a X there not x,still showing the error saying not enough input arguments

11. Hey Akshay, The error 'y' undefined problem do exist, but it is not othe problem only for the code you gave,any solution the internet gives that error.Even running through gui or through command, it says undefined.There is no clear solution for this on the net, I tried adding path too as it was said in the net.Couldnt solve the issue.I have octave 5.1.0

1. I found the solition for those who were getting u defi ed error.
if you are using octave
then
the file shouldnot first start with function, octave takes it as a function, not as a script.

solution
example
add 1; first line and then start function.

If you wanna test your function when you run, first initialize the variables to matrices and respective values.
then pass these as parameters to the function.

2. Thanks Chethan,
It will be a great help for others as well.

3. I didn't understand.can u explain clearly

4. include two lines of code

x=[];
y=[];

This should work

5. Its still not working. I'm getting:
error: 'y' undefined near line 7 column 12
error: called from
computeCost at line 7 column 3

12. Hi Akshay,
I am getting error like this
m=lenght(y); %number of training example

Can you help me

Thanks

13. أزال أحد مشرفي المدونة هذا التعليق.

14. Hello, within gradientDescent you use the following code

error = (X * theta) - y;
theta = theta - ((alpha/m) * X'*error)

What is the significance of 'error' in this? Within Ng's lectures I can't remember him making reference to 'error'

1. Error is similar to that of "cost" (J)

15. !! Submission failed: 'data' undefined near line 19 column 18

LineNumber: 19

This is my problem how to correct it

1. Hi, I think you are doing this assignment in Octave and that's why you are facing this issue.

Chethan Bhandarkar has provided solution for it. Please check out the comment by Chethan Bhandarkar: https://www.apdaga.com/2018/06/coursera-machine-learning-week-2.html?showComment=1563986935868#c4682866656714070064

Thanks

16. Code that is given is not running as always give error 'y' undefined near line 7 column 12 for every code.

1. Hi, I think you are doing this assignment in Octave and that's why you are facing this issue.

Chethan Bhandarkar has provided solution for it. Please check out the comment by Chethan Bhandarkar: https://www.apdaga.com/2018/06/coursera-machine-learning-week-2.html?showComment=1563986935868#c4682866656714070064

Thanks

2. did the same as of chethan said but still the issue is not resolved getting the same error y not defined

3. @Shilp, I think, You should raise your concern on Coursera forum.

error: 'y' undefined near line 7 column 12
error: called from
gradientDescent at line 7 column 3
>> computeCost()
error: 'y' undefined near line 7 column 12
error: called from
computeCost at line 7 column 3
i am getting this kind of error how to solve this

18. hey
i think the errors related to undefined variables are due to people not passing arguments while calling the func from octave window. Can you post an example of command to run computeCost with arguments

19. the Predicted prices using normal equations and gradient descent are not equals
(NE price= 293081.464335 and GD price=289314.62034) is it correct ?

1. I had the similar issue. For persons who would have a same situation later, please change your alpha to 1.0 and your iterations to 100.

20. For compute.m function, i am continuosly getting below error message:
Error in computeCost (line 31)
J = (1/(2*m))*sum(((X*theta)-y).^2);

1. What error you are getting exactly?

21. what is the predicted value of house..mine it is getting \$0000.00 with huge theta value how is that possible?

1. You have to modify the value of price variable in the ex1_multi file

22. Ok so for the people facing problem regarding y is undefined error.....you can directly submit the program it tests ex1.m file as a whole and it is compiled successfully and gives the correct answer

1. how can i directly submit the ex1.m file?

23. plotData
Not enough input arguments.

Error in plotData (line 19)
plot(x, y, 'rx', 'MarkerSize', 10); % Plot the data

I got this error. how can I solve this?

24. not enough input arguments.

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

1. I got the same error. have you found out a solution yet?

25. Hi, I am getting the same error and the program doesn't give the solution. Please advise.

26. Having problems with nearly everyone of these solutions. I am 12 and learning machine learning for the first time and having troubles referring to this as i find these solutions do not work. Any help?

27. Hello I am stuck in WK2 PlotData
I keep getting errors: >> Qt terminal communication error: select() error 9 Bad file descriptor like that one
or
error: /Users/a69561/Desktop/machine-learning-ex1/ex1/plotData.m at line 19, column 3

Can somebody help me ??

28. thank you for the solution but i m still getting 2 different values of price of house( with normal equation and gradient descent method)

30. Whats is your leaning rate alpha and number of iterations?

1. I have provided only function definitions here.
You can find the parameter (alpha, num of iterations) values in execution section of your assignment.

31. In Linear regression with multiple variables by 1st method ( gradientDescent method) the price value of the house was different whn compared to the 2nd method(Normal Equations).still not able to match the values of both the methods ?

Note : i have copied all the code as per your guidance.

32. hi, thanks for all your help. But I have some problem in submission. When I finished all work, I tried to submit all in once and got this:
>> submit
Warning: Function Warning: Name is nonexistent or not a directory: /MATLAB Drive/./lib
> In path (line 109)
In submit (line 2)

Warning: Function Warning: Name is nonexistent or not a directory: /MATLAB Drive/./lib/jsonlab
> In path (line 109)
In submitWithConfiguration (line 2)
In submit (line 45)

'parts' requires one of the following:
Automated Driving Toolbox
Robotics System Toolbox
Sensor Fusion and Tracking Toolbox

Error in submitWithConfiguration (line 4)
parts = parts(conf);

Error in submit (line 45)
submitWithConfiguration(conf);

>> submit
>> submitWithConfiguration
Warning: Function Warning: Name is nonexistent or not a directory: /MATLAB Drive/./lib/jsonlab
> In path (line 109)
In submitWithConfiguration (line 2)

'parts' requires one of the following:
Automated Driving Toolbox
Robotics System Toolbox
Sensor Fusion and Tracking Toolbox

Error in submitWithConfiguration (line 4)
parts = parts(conf);

1. Check if your are in the same directory ex1 folder and to submit the solution use ''submit()'' not submit add parenthesis

2. This is happening because variable parts has the same name as of parts(conf) function in file ex1/lib/submitWithConfiguration.m

Make the following changes to resolve this :
Line 4 - parts_1 = parts(conf);
Line 92 - function [parts_1] = parts(conf)
Line 93 - parts_1 = {};
Line 98 - parts_1{end + 1} = part;
Basically, I've just renamed the variables.
Same thing is happening with one more variable, so make the following changes :
Line 66 - submissionUrl_1 = submissionUrl();
Line 68 - responseBody = getResponse(submissionUrl_1, body);

Line 22: response = submitParts(conf, email, token, parts_1);
Line 37: showFeedback(parts_1, response);

This worked for me.

33. Hello Akshay,
In computeCost, how to declate or compute 'theta' because, it's giving an error - 'theta' undefined.

34. error: structure has no member 'message'
error: called from
submitWithConfiguration at line 35 column 5
submit at line 45 column 3
error: evaluating argument list element number 2
error: called from
submitWithConfiguration at line 35 column 5
submit at line 45 column 3
how to solve this

35. Hello Akshay Daga (APDaga,
Very glad to come across your guide on ML by Andred NG.

I been stuck months, could complete the Programming Assisgment.
Have done up to computeCost but got stuck at gradientDescent

Below is the error. I don't want to drop out of this course please help me out.

"error: 'num_iters' undefined near line 1 column 58"

Here is my update
h=(theta(1)+ theta(2)*X)';
theta(1) = theta(1) - alpha * (1/m) * theta(1) + theta(2)*X'* X(:, 1);
theta(2) = theta(2) - alpha * (1/m) * htheta(1) + theta(2)*X' * X(:, 2);

36. Hello Akshay Daga (APDaga,
Very glad to come across your guide on ML by Andred NG.

I been stuck months, could complete the Programming Assisgment.
Have done up to computeCost but got stuck at gradientDescent

Below is the error. I don't want to drop out of this course please help me out.

"error: 'num_iters' undefined near line 1 column 58"

Here is my update
h=(theta(1)+ theta(2)*X)';
theta(1) = theta(1) - alpha * (1/m) * theta(1) + theta(2)*X'* X(:, 1);
theta(2) = theta(2) - alpha * (1/m) * htheta(1) + theta(2)*X' * X(:, 2);

error: 'y' undefined near line 7 column 14
error: evaluating argument list element number 1
error: called from:

I am getting this error for both gradient descent and computeCost. plz helpme out

1. Hi, I think you are doing this assignment in Octave and that's why you are facing this issue.

Chethan Bhandarkar has provided solution for it. Please check out the comment by Chethan Bhandarkar: https://www.apdaga.com/2018/06/coursera-machine-learning-week-2.html?showComment=1563986935868#c4682866656714070064

Thanks

38. function [theta, J_history] = gradientDescent(X, y, theta, alpha, iterations)
% taking num_iters gradient steps with learning rate alpha

% Initialize some useful values
m = length(y); % number of training examples
h=X*theta;
error=(h-y);
theta_c=(alpha/m)*(sum((error)*X'));
theta=theta-theta_c;
J_history = zeros(num_iters, 1);

for iter = 1:iterations

% ====================== YOUR CODE HERE ======================
% Instructions: Perform a single gradient step on the parameter vector
% theta.
%
% Hint: While debugging, it can be useful to print out the values
% of the cost function (computeCost) and gradient here.
%

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

% Save the cost J in every iteration
J_history(iter) = computeCost(X, y, theta);

end

end

while running on octave it's showing
error: gradientDescent: operator *: nonconformant arguments (op1 is 97x1, op2 is 2x97)
error: called from
gradientDescent at line 10 column 8
ex1 at line 77 column 7

where is the problem???

39. i got an error in computeCost.m as following:
max_recursion_depth reached.
How to solve this?

40. i got an error as:
error: computeCost: operator /: nonconformant arguments (op1 is 1x1, op2 is 1x2)
How to solve this?

1. I can't see any variable used in codes as op1 or op2.

Please check once again where did you get those variables from?

41. Hi, great guidance. Only, I still have the confusion how single parameter costfunction and multi parameter costfunction codes are same? (same confusion for both gradientdescent (single and multi).Am I missing something?

1. single parameter costfunction is as follows:
h = X*theta;
temp = 0;
for i=1:m
temp = temp + (h(i) - y(i))^2;
end
J = (1/(2*m)) * temp;

Which doesn't work for multi parameter costfunction.

But, I have also provided vectorized implementation. (It is generic code and works for both single as well as multi parameters).

42. Hello,
I am getting x is undefined while submitting plotData in assignmnet2 several times I checked But I am getting the same error will u please help me?

43. function plotData(x, y)
plot(x, y, 'rx', 'MarkerSize', 10);
ylabel('Profit in \$10,000s');
xlabel('Population of City in 10,000s');

Always I am getting x is undefined.I cant able to understand where the error is plzz help me??

figure;

44. function plotData(x, y)
plot(x, y, 'rx', 'MarkerSize', 10);
ylabel('Profit in \$10,000s');
xlabel('Population of City in 10,000s');
figure;

Always I am getting x is undefined.I cant able to understand where the error is plzz help me??

1. Hi, I think you are doing this assignment in Octave and that's why you are facing this issue.

Chethan Bhandarkar has provided solution for it. Please check out the comment by Chethan Bhandarkar: https://www.apdaga.com/2018/06/coursera-machine-learning-week-2.html?showComment=1563986935868#c4682866656714070064

Thanks

2. While doing in matlab also it is saying error in submitwithconfiguration in submit.m file accutally it was defaultly givern by them but why it is show error there???

45. While doing in matlab it is saying error in submitwithconfiguration in submit.m file accutally it was defaultly givern by them but why it is show error there???

46. Still the same problem with undefined y (small letter) using Octave 5.2.0

adding anything as first line didn't help

What could I do else? Has somebody working version. I got stuck in this point

1. instead of running codes individually, run 'ex1' after completing all the problems....then it will not show any error

47. Hi..
I am using MATLAB R2015a version offline and getting error submitwithconfiguration(line 158).How to rectify this error??

1. Raise this concern in Coursera forum.

48. if you implement featureNormalize this way, it gives dimensions disagreement error so i suggest it would be better to do it in the following way;

mu = ones(size(X,1),1)* mean(X);
sigma = ones(size(X,1),1)* std(X);
X_norm = (X - mu)./(sigma);

P.S: it gives me accurate results

49. I entered submit () ,but I geeting error so pls help to how to submit my assignment

1. I think you should raise this concern to Coursera forum.

2. try just submit without the brackets.

50. ur code is not working when i use it

1. Sorry to know that. But I was working 100% for me and some others as well.

51. num_iters not defined error.. Plz help

52. just got the answer for num_iters not defined...You have to fix line 59 in submit.m

53. I have a problem running the below line of code:

(X * theta) - y;

it gives error: operator *: nonconformant arguments (op1 is 97x1, op2 is 2x1)

I can understand because X is a 97x1 matrix and cannot be multiplied with a 2x1 matrix. Any ideas?

54. I get the below error when executing ex1 for testing the gradientDescent function:

error: computeCost: operator *: nonconformant arguments (op1 is 97x2, op2 is 194x1)
error: called from
computeCost at line 15 column 2
gradientDescent at line 36 column 21
ex1 at line 77 column 7

My gradientDescent function has the below lines of code as per the tutorial.

temp0 = theta(1) - ((alpha/m) * sum((X * theta) - y) .* X(:,1));
temp1 = theta(2) - ((alpha/m) * sum((X * theta) - y) .* X(:,2));
theta = [temp0; temp1];

My computeCost function has this line of code on line number 15:

J=1/(2*m)*sum(((X*theta)-y).^2)

NB: surprisingly I can run the gradientDescent lines individually on octave command without problems

1. I also had this problem, I realised that it is to do with the brackets.
if you compare your code to mine;

t0 = theta(1) - ((alpha/m) * sum(((X * theta) - y).* X(:,1)));
t1 = theta(2) - ((alpha/m) * sum(((X * theta) - y).* X(:,2)));
theta = [t0; t1];

you can see that you are missing 2 brackets on each side. this dimensions may be messed up due to wrong operations

55. Hey, how do you calculate the value of theta?

1. The values of theta1 and theta2 are initially set to 0, theta = zeros(2,1)

56. Getting an error, theta is undefined...

57. I get the below error when executing ex1 for Submitting the gradient Descent:
>> submit
'parts' requires one of the following:
Automated Driving Toolbox
Robotics System Toolbox
Sensor Fusion and Tracking Toolbox

Error in submitWithConfiguration (line 4)
parts = parts(conf);

Error in submit (line 45)
submitWithConfiguration(conf);

1. did you get this answer? , I see this error

2. I have the same error

58. some of these answers are incorrect. for example the feature normalization question is wrong. when you calculate X-u /sigma X and u are different dimensions so it doesn't work.

1. Thanks for the feedback.
All these answers worked 100% for me. and they are working fine for many of others as well (you can get idea from comments.)
But coursera keeps on updating the assignments time to time. So, You might be right in that case.
Thanks

59. hello brother, can you please briefly explain the working in these two lines of GD
error = (X * theta) - y;
theta = theta - ((alpha/m) * X'*error)

60. How can I solve this problem??
submit
'parts' requires one of the following:
Automated Driving Toolbox
Robotics System Toolbox
Sensor Fusion and Tracking Toolbox

Error in submitWithConfiguration (line 4)
parts = parts(conf);

Error in submit (line 45)
submitWithConfiguration(conf);

61. same problem here

62. Hi, when I run my code, the predicted price of the house (in ex1_multi.m), it says 0.0000. How can I fix that?

63. >> [Xn mu sigma] = featureNormalize([1 ; 2 ; 3])
error: Invalid call to std. Correct usage is:

-- std (X)
-- std (X, OPT)
-- std (X, OPT, DIM)
error: called from
print_usage at line 91 column 5
std at line 69 column 5
featureNormalize at line 32 column 8
>>
Even after I am doing it the right way i hope:
'''
mu = mean(X);
sigma = std(X, 1);
X_norm = (X - mu) ./ std;
'''

Anyone any idea, why i am facing this error?

1. I tried simply this also:
sigma = std(X);

64. >> submit()
'parts' requires one of the following:
Automated Driving Toolbox
Robotics System Toolbox
Sensor Fusion and Tracking Toolbox

Error in submitWithConfiguration (line 4)
parts = parts(conf);

Error in submit (line 45)
submitWithConfiguration(conf);

1. This is happening because variable parts has the same name as of parts(conf) function in file ex1/lib/submitWithConfiguration.m
Make the following changes to resolve this :
Line 4 - parts_1 = parts(conf);
Line 92 - function [parts_1] = parts(conf)
Line 93 - parts_1 = {};
Line 98 - parts_1{end + 1} = part;
Basically, I've just renamed the variables.
Same thing is happening with one more variable, so make the following changes :
Line 66 - submissionUrl_1 = submissionUrl();
Line 68 - responseBody = getResponse(submissionUrl_1, body);

Line 22: response = submitParts(conf, email, token, parts_1);
Line 37: showFeedback(parts_1, response);

This worked for me

65. which is better to use to submit assignments ( Octave or Matlab)... The solutions that have been provided are for Matlab or Octave?

1. I have provided solution in MATLAB but It works in Octave as well.

66. hi I don't understand why X*theta . I mean theta is a 2X1 vector right? I understand the formula, but i get confused in this exercise.

1. I figure it out because I thought X is a 97x1 vector. I have another question. Is this a gradient descent with one variable? I thought it is two variables? Does the theta0 count 1 variable?

67. %%%%%%%% CORRECT %%%%%%%%%%
error = (X * theta) - y;
theta = theta - ((alpha/m) * X'*error);
%%%%%%%%%%%%%%%%%%%%%%%%%%%
WHY IS NOT HERE "SUM" USED? THAAAAAAAANKS!!!

1. Here we have used a Matrix multiplication (Which is nothing but Sum of product operation).
Matrix multiplication already consist of sum operation.

2. OWWWWWWWW!!! so the other one is (dot product). Thank you so much! You are awesome !

3. J = (1/(2*m))*sum(((X*theta)-y).^2);
Can you please break it down, then we used SUM here. Thanks in advance !!

4. and not in the above one (theta = theta - ((alpha/m) * X'*error))?

Like I could see with the dimensions that, sum is not required.
But I want to know how should I think/(the intuition) or approach to this idea that I need or dnt need sum.

5. "Matrix multiplication (Which is nothing but Sum of product operation)." then why using SUM here, J = (1/(2*m))*sum(((X*theta)-y).^2);

7. Don't get confused with normal and vectorized implementation.
> "sum" in vectorized implementation represents summation in the given formula.
> In normal implementation, "temp = temp + formula" is equivalent to that of "sum" in vectorized implementation.

Please look at below code, (both codes achieves same result) compare them and try to understand.

%%%%%%%%%%%%% CORRECT %%%%%%%%%
% h = X*theta;
% temp = 0;
% for i=1:m
% temp = temp + (h(i) - y(i))^2;
% end
% J = (1/(2*m)) * temp;
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

%%%%%%%%%%%%% CORRECT: Vectorized Implementation %%%%%%%%%
J = (1/(2*m))*sum(((X*theta)-y).^2);
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%

8. My Goodness ! Thank you so much! You are awesome ! You have explained it very nicely! Became your fan. God bless you! Will be following your Blog.

68. x = data(:, 1); y = data(:, 2);
m = length(y);
plot(x, y, 'rx', 'MarkerSize', 10);
ylabel('Profit in \$10,000s');
xlabel('Population of City in 10,000s');
X = [ones(m, 1), data(:,1)];
theta = zeros(2, 1);
iterations = 1500;
alpha = 0.01;
temp = 0;
for i=1:m
temp = temp + (h(i) - y(i))^2;
end
J = (1/(2*m)) * temp;

>> J
J = 32.073 the answer is good

But when execute the submit:

!! Submission failed: operator *: nonconformant arguments (op1 is 97x1, op2 is 2x1)

Function: computeCost
FileName:
LineNumber: 65

69. WHY IT IS SHOWING "This item will be unlocked when the session begins." ON THE QUIZ SECTION.

70. managed to run every other thing corectly in octave but got a submission error.please help( !! Submission failed: parse error near line 25 of file C:\Users\user\Desktop\ml-class-ex1\computeCostMulti.m)

syntax error

>>> j= (1/(2*m)) *sum(((X*theta)-y.^2);
^

Function: submit>output
FileName: C:\Users\user\Desktop\ml-class-ex1\submit.m
LineNumber: 63

> submit
Unrecognized function or variable 'parts'.

Error in submitWithConfiguration (line 4)
parts = parts(conf);

Error in submit (line 45)
submitWithConfiguration(conf);

72. i have some issues while uploading codes. i do run it without any error but at the end the score still shows 0/10 for 3rd questions and so on. Along with this the same result reflects on my course id. Please help

1. It should not happen. you might be missing something simple in your process.
have you raised this concern on coursera forum. please try it there, you will get the resolution for sure.

73. I have error at m= length(y)

This error is occur

74. Thank you Akshay for your helping lots of people for years!

1. Thank you for your kind words.

75. Hi Akshay i have question about gradient descent with multiple variables.
Q(0) Q(1)
While doing the Gradient descent we were using X as [1 random number]
[1 random number]
[1 random number]

we were using 1 for Q(0).
My question is for doing multiple varient Gradient Descent do we use X matrix as a
Q(0) Q(1) Q(2)....
X = [1 random random ...]

because in coursera as an example they took as;
X = data(:, 1:2);
y = data(:, 3);

Don't they need to add 1 numbers in X for to represent Q(0)?

1. Once you split the input(X) and output(y) from the raw data.
The below line add the 1 in the input =(X) as mentioned the theory.

x = [ones(m, 1), data(:,1)]

Above line will take care of adding one in the input(X). Please check the code, it is already present in the code.