isequal(mysort(A)

1、IT1005,Lab session on week 9 (5th meeting),Good Friday and Happy Easter to all students,especially for those who understand the meaning and celebrate these events . Since Friday is a public holiday, students with lab sessions on Friday are advised to attend parallel lab sessions on the other days!,Lab 5 Quick Check,Have you all received my reply for lab 5? My reply should contains: Your M files Check your files for my comments, look for this tag “SH7: bla bla bla”. Use CTRL+F (Find feature) of y

2、our text editor to quickly identify my SH7 tags. Your Microsoft Word file Only if you do not give me your M files. Most of my comments will be in the M files. Anyway, check my comments here, if any, especially for q1.c and q2.b. IMPORTANT: PLEASE DO NOT SEND ME DUPLICATE STUFFS!IF YOU SEND M FILES, DO NOT COPY THE CODE TO MS WORD FILE! Your marks is stored in the file “Marks.txt” inside the returned zip file! If there is something wrong with the marks, clarify it with me. Either under counting o

3、r over counting. I have been quite lenient in the past few labs, next time I will be stricter.,L5.Q1.a: my_mean (standard),function theMean = my_mean(x) % let us name the input array as x. % if you want to explain something about this function, here is the best place! theSum = 0; % do not use name sum, as it is a default Matlab function name n = numel(x); for index = 1:n % sum everything from index 1 to last (note: there are other ways to do this loop) theSum = theSum + x(index); end theMean = t

4、heSum / n; % return the average a.k.a. mean % Notice that we suppress ALL intermediate outputs with ;! % Our function should be clean!,L5.Q1.a: my_mean (geek),function theMean = my_mean(x) theMean = sum(x(:) / numel(x); % x(:) will give me an enumeration of the input array x (whatever dimension) into column vector % Doing x(:) will definitely give me a row vector % Thus, this trick will work for array of ANY dimension =) % sum will then work for this row vector. % Note that there is this line in

5、 the lab 5 question 1.a. % You are NOT ALLOWED to use the MATLAB mean command, % and should instead use loops, etc (Matlab function sum is ok) to implement your function. % Very short, eh =).,L5.Q1.b: my_var (standard),function theVar = my_var(x) % We should just call our my_mean function here. Do not create it again (redundant!). % Store the result in a variable so that we do not re-count mean every time! (Important!) theMean = my_mean(x); n = numel(x); sumOfSD = 0; % sum of squared deviation!

6、for index = 1:n % accumulate the sum of squared deviation sumOfSD = sumOfSD + (x(index) - theMean)2; end theVar = sumOfSD / (n-1); % you know why we divide this with n-1 right?,L5.Q1.b: my_var (geek),function theVar = my_var(x) theVar = sum(x(:) - my_mean(x) . 2) / (numel(x) - 1); % If you do not understand why that works, see these: % 1. Convert input array x into a row vector = x(:) % 2. Find the difference with the mean, scalar expansion! = x(:) - my_mean(x) % 3. Square the differences = (x(:

7、) - my_mean(x) . 2 % 4. Sum the squared differences = sum(result of part 3 above) % 5. Divide the result in step 4 above with n 1,L5.Q1.c: (Crazy) Testing,% Many ways to do this, as long as you can show that your program is correct. % My way: There are mean and var commands in Matlab, let us compare with them THOROUGHLY! % mean and var(iance) are floating points, we must use floating point comparison! % Tests with MANY inputs, the best is to use random function :D, thorough test with minimum wor

8、k for test = 1:100 % can increase this if you want :p, this is called stress test in Software Engineering A = randn(1,100); % just generate a big random array, every time the array is different result1 = abs(my_mean(A) - mean(A(:) eps); % CANNOT just say my_mean(A) - mean(A(:) ! result2 = abs(my_var(A) - var(A(:) eps); % We MUST test the ABSOLUTE difference! if result1 = 1 | result2 = 1 disp(sprintf(Test %d: WARNING, your program is still WRONG!, test); else disp(sprintf(Test %d: OK, test); end

9、end,L5.Q1.d: Using randn,length = input(Enter the length of the random normalized array: ); arr = randn(1,length); % Random row array with mean near 0, variance near 1! theMean = my_mean(arr); theVar = my_var(arr); % Since the question wants the ans = to be printed, I use sprintf here! sprintf(The actual mean is %g and the actual variance is %g. Therefore the mean is off by %g, and the variance is off by %g., . theMean, theVar, abs(theMean), abs(theVar-1.0) % Do not write ; here! % for mean, you do not need to say abs(theMean-0), the -0 part is redundant,L5.Q2.a: my_sort.m (standard),function d = my_sort(x) % assume the input array x is a row vector d = x; % copy x to d first, d is the variable that holds our answer! n = numel(x); % as mentioned in lab hint. no change at all. for i = 1:n for j = 1:(n-1) if d(j) d(j+1) tmp = d(j); % need to store this in a temporary variable first d(j) = d(j+1); % otherwise the value of d(j) is gone after

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