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IT1005 Lab session on week 8 (4 th meeting) Say No to Plagiarism.

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Presentation on theme: "IT1005 Lab session on week 8 (4 th meeting) Say No to Plagiarism."— Presentation transcript:

1 IT1005 Lab session on week 8 (4 th meeting) Say No to Plagiarism

2 Submission System (Review) Good, just one-two “ subject” violations for lab 4. – For those who are still blur, write “IT1005-2B YourName” in your subject! This helps my Gmail to auto sort your submissions. Now, I have one more request. – For lab 5, instead of naming “u0xxxxxx-lab5.zip”,write in your name! “StevenHalim.zip”, “StevenHalim.doc”, “StevenHalim_q51.m”, “StevenHalim_q52.m”, “my_mean.m”, “my_var.m”, “my_sort.m”, “my_sort2.m”. Ignore Colin’s instruction, I am using my own standard here. DO NOT COPY THE INDIVIDUAL *.m FILES INTO *.doc! – No need to send me duplicate things >.< – Your MS-Word file will just contain ‘explanation’ of your code. – Or you can just embed that explanation as comments inside your m files, no need to send me an MS-Word file for this lab… – Reason: I cannot grade one student per student, too slow… It is better/faster to grade one question per question… So I need to download your files individually anyway. With so many files for lab 5, it will be a chaos if all of them are ‘u07xxxxx’! ><

3 Lab 4 – Plagiarism What are NOT ok? – Blindly/partially copy your friend’s M-file/MS-Word file with/without his/her consent! – ‘Just’ looking at other student’s MS-Word file, your answer will then tend to follow his/hers, especially if you are not sure with your own answer… – Working together to create the M-file, then copy-paste the SAME M-file to each of your MS-Word files. – Blind/partial copy from past year solution... It happens for lab 4 q2, q3, and q4. Anyway, past year solution is not always 100% correct according to current grader (me)… What are ok? – Gentle discussion: there is only thin line between plagiarism and proper discussion. – Positive discussion is ok, and it helps learning. – After ‘gentle’ discussion, you must type in Matlab code from scratch by yourself! – From your discussion, create two different Matlab programs that do the same thing! That shows me that you really understand what you are doing. This is a strong warning for Lab 4! – No more mercy for lab 5 onwards! – Plagiarism will just make your life more difficult for upcoming labs/assignment/final exam! – Note that labs is just 10%, midterm test is 20%, assignment is 30%, final is 40%! Say No to Plagiarism

4 Lab 4 – Quick Check Have you all received my reply for lab 4? – My reply contains: Your Microsoft Word file With my comments, and Your marks. – If there is something wrong with the marks, clarify it with me. – Note that your file is renamed to YOUR matriculation card name. – Help me by naming your files for lab 5 (the zip file, the Microsoft Word file) with your name! See the previous two slides for details.

5 Lab 4 – Answers (Q1) Q1 – Mastering the command ‘find’ A.[r c] = find(F < -0.8) B.Either you write 4 coordinates: (2,1) (2,2) (1,3) (2,3), or you create program to enumerate these. for index=1:numel(r) % if r has 4 elements, it will display 4 lines disp(sprintf('(%d, %d)', r(index), c(index))); end C.[r c] = find(-1 -1 % as it clearly shows the range that F is in. % The resulting coordinates (not asked): (2,2) (1,3) (2,3).

6 Lab 4 – Answers (Q2) Q2 – for loop versus while loop A.Observations: Loops ‘max’ number of times, each time prints the value of i and cnt, then finally prints the value of cnt / i. When swapped, ‘i' tells the value of ‘cnt’ in scientific notation (cannot print floating point using %d), ‘cnt’ tells the value of ‘i‘, which is not really correct if you just look at the output. The final value of ‘cnt’/i does not change since the physical ‘cnt’ actually never altered! ‘\n’ is newline character. B.While loop version of the same program: 1.max = input( ' please enter maximum count: ' ); 2.cnt = 0; i = 1; % must set the initial value 3.while i <= max % keep looping while this statement is still true 4. cnt = cnt * i; % if you start from i = 0; do i = i + 1; before executing this line! 5. sprintf( ' i is %d and cnt is %g\n ', i, cnt) 6. i = i + 1; % must do this so that after looping ‘max’ number of times, condition in line 3 is no longer true. 7.end 8.cnt = cnt / (i - 1); % we will over count by one after exiting the while loop! Alternative: loop from 0 to < max! 9.sprintf( ' cnt divided by i gives %g\n ', cnt) C.Differences are the one highlighted in part b above. See the comments there. Some of you are not really answering the question: for loop is “bla bla”, while loop is “bli bli”. The context is q2b! Say that the while loop version needs to have i initialized to 1 outside the loop, incremented by one inside the loop, and stopped when i <= max, it will be over count by 1 at the end, etc…

7 Lab 4 – Answers (Q3-standard) % This may be your first ever Matlab program with repetition control flow. num = 0; denom = 0; n = input('Please enter the number of modules: '); % with just ONE loop, you can get input, and compute the results simultaneously. Assume VALID inputs! for moduleID = 1:n % it is better to use ‘for loop’ as we know how much to count here (1 to n). % use meaningful variable name, e.g. ‘MC’, ‘grade’, rather than ‘f’, ‘s’ (do not follow the lab hints too much >.<)? MC = input(sprintf('Please enter the modular credit for module %d: ', moduleID)); % denom can already be updated now. % num must be latter, since it requires both ‘MC’ and ‘grade’(sequence issue!) denom = denom + MC; grade = input(sprintf('Please enter the grade point for module %d: ', moduleID)); num = num + MC * grade; end cap = num / denom; disp(sprintf('CAP = %g\n', cap)); % better use ‘disp’ so that the ‘ans’ is not printed!

8 Lab 4 – Answers (Q3+protection) num = 0; denom = 0; n = 0; % initialize n properly! while n < 1 n = input('Please enter the number of modules (integer >= 1): '); end for moduleID = 1:n MC = -1; grade = -1; % initialize MC and grade properly! while MC < 1 MC = input(sprintf('Please enter the modular credit (integer >=1) for module %d: ', moduleID)); end denom = denom + MC; while grade ~= (0:0.5:5) % complex statement, this is to test whether grade is one of the valid option? grade = input(sprintf('Please enter the grade point (floating point within [ ]) for module %d: ', moduleID)); end num = num + MC * grade; end cap = num / denom; disp(sprintf('CAP = %g\n', cap)); Good that some of you remember that I have mentioned extreme cases during lab 0/1 (the division by zero stuff).

9 Lab 4 – Answers (Q4-standard) % This may be your first ever Matlab program with decision control flow. … continued from q3% Please… DO NOT give me the answer for q3 again! Redundant! % Either write this line “continued from q3” or just combine your q3 and q4 answers! % use if-elseif-elseif-elseif-end rather than using nested if-else-end (too skewed to the right and you may confused with ‘end’s!) if cap > 4.5 % what if cap == 4.5? disp( ' Genius!! ' ); elseif cap >= 4.0 & cap < 4.5% is this cap < 4.5 needed? disp( ' Pretty darn smart!! ' ) elseif cap >= 3.5 & cap < 4.0 disp( ' Smart! ' ); elseif cap >= 3.0 & cap < 3.5 % how to explain the overlapping ranges? disp( ' Quite Clever! ' ); elseif cap >= 3.2 & cap < 3.5 % this is subset of the above disp( ' Clever! ' ); elseif cap >= 2.5 & cap < 3.2% 3.0 – 3.2 are already classified as ‘Quite Clever!’ above disp( ' Hmmm… ' ); elseif cap >= 2.0 & cap < 2.5 disp( ' Ohh need to work harder! ' ); elseif cap < 2.0 disp( ' Oops.. ' ); end

10 Lab 4 – Answers (Q4-better) … continued from q3 if cap >= 4.5 % what if cap == 4.5? Assume it is genius (first class), cap value cannot be > 5.0 anyway disp('Genius!!');% if our previous inputs are valid (see slide 7, q3+protection). elseif cap >= 4.0% cap < 4.5 is NOT needed as it is true if it does not fit into the first case above! disp('Pretty darn smart!!') elseif cap >= 3.5 disp('Smart!'); elseif cap >= 3.2 % reordered, ‘Clever!’ is cleverer than ‘Quite Clever!’ disp('Clever!');% new range = [ ) elseif cap >= 3.0 disp('Quite Clever!'); % new range = [ ) elseif cap >= 2.5 disp('Hmmm…'); % new range = [ ) elseif cap >= 2.0 disp('Ohh need to work harder!'); else% obviously this case is cap < 2.0 disp('Oops..'); end % Note: there are other ways to answer this question, all are ok as long as proper assumption is given!

11 The Art of Indentation (1) Indentation depth = 1 tab, 2/3/4 spaces – It is a matter of style, stick with one and be consistent! Increase the indentation level after – Decision statements (‘if’, ‘switch’), or – Repetition statements (‘for’, ‘while’)! Decrease the indentation level – As soon as you hit an ‘end’ statement. If you still unsure, study the next few slides!

12 The Art of Indentation (2) Wrong Example Too flat: a = 2; if a >= 1 b = 0; while b < 7 disp(‘hey’); b = b + 1; end disp(‘last line’); Wrong Example Zig Zag: a = 2; if a >= 1 b = 0; while b < 7 disp(‘hey’); b = b + 1; end disp(‘last line’);

13 The Art of Indentation (3) Wrong Example Indenting if/while: a = 2; if a >= 1 b = 0; while b < 7 disp(‘hey’); b = b + 1; end disp(‘last line’); Wrong Example Wrong match: a = 2; if a >= 1 b = 0; while b < 7 disp(‘hey’); b = b + 1; end disp(‘last line’);

14 The Art of Indentation (4) Wrong Example Too many white spaces: a = 2; if a >= 1 b = 0; while b < 7 disp(‘hey’); b = b + 1; end disp(‘last line’); Good Example Balanced, neat: a = 2; if a >= 1 b = 0; while b < 7 disp(‘hey’); b = b + 1; end disp(‘last line’); Indentation level 0 Indentation level 1 Indentation level 2

15 Review on Functions So far, codes that we have written reside in ONE M-file only. – As the code getting more complex, it can be very messy. We need to ‘modularize’ them into logical functions. – Group of codes that can be reused again in the future. Example of functions that we have used so far: – sin, cos, abs, input, disp, sort, max, min, etc. The syntax is easy, just remember this: function returnValue = functionName(argument1, argument2,…,argumentN) % If you want to add help messages, write it here. Separate it with blank line! % Write your Matlab codes here, get the arguments, process them, return the result! % Usually, functions do NOT ask for input/print output! (exception: input, sprintf, etc) % Usually, we suppress all the ‘intermediate’ output by giving ‘;’ at every line returnValue = finalValue; % assign the result to this variable (returned to caller)! Save the function into a new M-file – With exactly the same file name as the function name! Input(s) to your function Output(s) of your function

16 Example (Related to Lab 5) Create a function “my_max.m” that given an array of numbers, return the maximum number inside the array. Example: – A = [ 1 3 ; 4 2 ]; % This is an example with 2-D array – % Not all Matlab commands behave similarly for 1-D (row array) versus 2-D! – my_max(A) – ans = – 4 Testing: – Compare our own implementation with Matlab’s default ‘max’! – my_max(A) == max(max(A)) % must do max(max(A)) for 2-D array! – my_max(A) == max(A(:)') % or do this, clever trick for any dimension! If ans = 1 for various types of A, likely that you have done it correctly =). If ans = 0 for an instance of A, then you are still wrong. This is ok since my input are all Integers – The test is different if the input is not integers! % test if absolute difference < eps

17 my_max.m function maxValue = my_max(inputArray) % my_max(inputArray) % This function will return the max element of inputArray % Only one argument will be accepted... % This is the last line of the help message... % Find the max element in inputArray maxValue = inputArray(1); % Assume that the first element is the max for index = 2:numel(inputArray) % Iterate through the rest to find the true max if inputArray(index) > maxValue maxValue = inputArray(index); end % Look, I do NOT assign returnValue = maxValue as the last line of my function % I can use maxValue (return value) like normal variable, highlighted in red :)

18 Lab 5 - Overview Sample Mean = sum all n items divided by n Sample Variance = (standard deviation) 2 = sum of squared deviation divided by (n – 1) – Not by ‘n’. There is a reason for this. *See Statistics textbook* Sorting – Given unsorted input, e.g. [ ]; – Do something with these numbers (sort it). – Return the sorted output of the input, e.g. [ ]; Bubble sort = one of the ‘easiest’ (but slow) sorting algorithm. – Google this term to study more! rand [ ] versus randn (normalized with mean 0, var 1). – randn(x) will give you n*n matrix of random numbers You need to do something else to create row array! % randn(1,number_of_columns)

19 Lab 5 – Free and Easy Time Now, you are free to explore Matlab, especially to find answers for Lab 5. No extra challenge this time >.< Let’s just focus on finishing lab 5 on your own, catch up if you are still behind, or to do your 30% term assignment. PS: Now we are entering the second half of the semester. Your lecturer have changed to Dr Saif Khan. And the topics shifted to ‘applications’ of Matlab.


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