# From what distribution does the `rand()` function return value? - [ ] normal - [ ] poisson - [ ] binomial - [x] uniform # Based on the code below, c is the \_ of a. ``` a = rand(1, 11); b = sort(a); c = b(1, ceil(end/2)); ``` - [x] median - [ ] mode - [ ] mean - [ ] margin # What does the Profiler track? - [x] execution time - [ ] command history - [ ] errors - [ ] the value of variables # Which code block contains the correct syntax for a `while` loop? - [ ] ``` a = 0; do a = a + 1; while a < 5 end ``` - [ ] ``` a = 0; while(a < 5) a = a + 1; ``` - [ ] ``` a = 0; while a < 5: a = a + 1; ``` - [x] ``` a = 0; while a < 5 a = a + 1; end ``` # What does `b` contain? ``` a = 19 20 12 0 6 6 9 56 0 3 46 8 9 8 19 9 8 8 19 46 1 9 46 6 19 ``` - [x] ``` b = 56 0 9 8 ``` - [ ] ``` b = 8 19 19 46 ``` # You have written a function `myfun` and want to measure how long it takes to run. Which code segment will return in `t` the time in seconds it takes `myfun` to run? - [ ] ``` t = cputime(myfun()); ``` - [x] ``` tic; myfun(); toc; ``` - [ ] ``` timer.start; myfun() t = timer.stop; ``` - [ ] ``` t = timer(myfun()); ``` # What is `%%` used for? - [ ] argument placeholder - [ ] block quotes - [x] code sections - [ ] conversion specifier # what is the `.` character NOT used for? - [ ] structure field access - [ ] a decimal point - [x] cell array access - [ ] element-wise operations # Which function could you use for multiple linear regression? - [ ] polyval - [x] regress - [ ] solve - [ ] polyfit # For which of these arrays do `mean`, `median`, and `mode` return the same value? - [x] [0 1 1 1 2] - [ ] [1 3 5 5 6] - [ ] [0 1 1 1 1] - [ ] [0 0 5 5 5] # You are in the middle of a long MATLAB session where you have performed many analyses and made many plots. You run the following commands, yet a figure window doesn't pop up on the top of your screen with your plot. What might be the issue? ``` x = [-1:0.1:1]; y = X.^2; plot(x, y) ``` - [ ] Your plot doesn't plot in a figure window because `figure` was not called immediately in advance. - [ ] Your `plot` syntax is incorrect. - [x] Your plot is in a figure window that was already open, hidden behind other windows on your screen. - [ ] Your plot was saved to an image file but not displayed. # How do you access the value for the field `name` in structure S? - [ ] S['name'] - [x] S.name - [ ] S('name') - [ ] S{'name'} # What built-in definition does i have? - [x] basic imaginary unit - [ ] index function - [ ] infinity - [ ] index variable # Which statement is equivalent to this for loop? ``` a = [1 2 3; 4 5 6]; b = zeros(size(a)); for i_row = 1:size(a, 1) for i_col = 1:size(a, 2) b(i_row, i_col) = a(i_row, i_col)^2; end end ``` - [ ] b = a\*a; - [x] b = a.^2; - [ ] b = a^2; - [ ] b = pow2(a); # You have plotted values of cosine from -10 to 10 and want to change the x-axis tick marks to every pi, from -3*pi to 3*pi. Which statement will do that? - [ ] xticks(-3*pi:3.14:3*pi) - [x] xticks(-3*pi:pi:3*pi) - [ ] xticks(linespace(-3*pi(), 3*pi(), pi())) - [ ] xticks(linespace(-3*pi, 3*pi, pi) # What is the value of `c`? ``` a = ones(1,3); b = 1:3; c = conv(a,b) ``` - [ ] [-1 2 -1] - [x] [1 3 6 5 3] - [ ] 6 - [ ] [1 -2 1] # Which function CANNOT be used to randomly sample data? - [ ] datasample - [ ] randi - [x] resample - [ ] randperm # Which choice is correct syntax for a `switch` statement? - [x] ``` x = 7; switch x case 2 disp("two"); otherwise disp("not two"); end ``` - [ ] ``` x = 7; switch x : case 2 disp("two"); otherwise disp("not two"); end ``` - [ ] ``` x = 7; switch x case 2 disp("two"); else disp("not two"); end ``` - [ ] ``` x = 7; switch x case 2 disp("two"); default disp("not two"); end ``` # What is the result of this code? ``` a = 1; b = 2; c = 3; d = 4; e = c / (~a - b == c - d); ``` - [ ] Error - [ ] ``` c = NaN ``` - [x] ``` c = Inf ``` - [ ] ``` c = -0.2500 ``` # What is true of a handle class object? - [ ] When you pass a handle object to a function, a new object is made that is independent of the original. - [x] All copies of handle objects refer to the same underlying object. - [ ] Handle object cannot reference one another. - [ ] Handle object do not have a default `eq` function. # Which choice has a different final result in `f10` than the other three? - [ ] ``` f10 = 1; for i = 1:10 f10 = f10 * i; end ``` - [ ] `f10 = factorial(10)` - [x] ```MATLAB f10 = 1; i = 1; while i <= 10 i = i + 1; f10 = i * f10; end ``` - [ ] `f10 = prod(1:10)` # Which choice will NOT give you a 5 x 5 identity matrix? - [ ] ``` a = rand(5); round(a * inv(a)) ``` - [ ] `diag(ones(5, 1))` - [x] `identity(5)` - [ ] `eye(5)` # Which statement creates this structure? ``` dog = name: 'Bindy' breed: 'border collie' weight: 32 ``` - [ ] `dog = struct('name', 'Bindy'; 'breed', 'border collie'; 'weight', 32);` - [x] ``` dog.name = 'Bindy'; dog.breed = 'border collie'; dog.weight = 32; ``` - [ ] ``` dog = { 'name' : 'Bindy', 'breed' : 'border collie', 'weight': 32; } ``` - [ ] ``` dog('name') = 'Bindy'; dog('breed') = 'border collie'; dog('weight') = 32; ``` # `my_func` is a function as follows. What is the value of `a` at the end of the code beneath? ``` function a = my_func(a) a = a + 1; end ------------------ a = 0; for i = 1:3 my_func(a); end a = my_func(a); ``` - [ ] 4 - [ ] 3 - [ ] 0 - [x] 1 # Which statement could create this cell array? ``` c = {["hello world"]} {1×1 cell} {["goodbye"]} {1×3 double} ``` - [ ] c = {"hello world" {"hello"} "goodbye" [1 2 ]}; - [ ] c = {"hello world" {"hello"} "goodbye" {[1 2 3]}}; - [x] c = {"hello world" {"hello"} "goodbye" [1 2 3]}; - [ ] c = {"hello world" {"hello" "hello"} "goodbye" {[1 2 3]}}; # Which choice adds `b` to each row of `a`? ``` a = ones(4, 4); b= [1 2 3 4]; ``` - [ ] a = a + reshape(b, 4, 1); - [ ] a = a + b'; - [x] a = a + repmat(b, 4, 1); - [ ] a = a + [b b b b]; # Which choice replaces all `a`s with `o`s? - [ ] ``` for i = 1:length(fruit) fruit{i}(fruit{i} == a) == o; end ``` - [ ] ``` for i = 1:length(fruit) fruit(i)(fruit(i) == 'a') == 'o'; end ``` - [x] ``` for i = 1:length(fruit) fruit{i}(fruit{i} == 'a') == 'o'; end ``` - [ ] ``` for i = 1:length(fruit) fruit{i}(fruit{i} == 'a') == 'o'; ``` # Which statement returns the roots for the polynomial `x^2 + 2x - 4`? - [ ] poly([1 2 -4]) - [ ] solve(x^2 + 2x - 4 == 0) - [ ] polyfit(x^2 + 2x - 4 == 0) - [x] roots([1 2 -4]) # Which choice is the proper syntax to append a new elements `a` to the end of 1x 2 dimensional cell array `C`? - [ ] C = {C a}; - [ ] C = cellcat(C a) - [ ] C = cat(2, {a}, C) - [x] C{end+1}=a # You have loaded a dataset of people's heights into a 100 x 1 array called `height`. Which statement will return a 100 x 1 array, `sim_height`, with values from a normal distribution with the same mean and variance as your height data? - [ ] sim_height = std(height) + mean(height) \* randn(100, 1); - [x] sim_height = mean(height) + std(height) \* randn(100, 1); - [ ] sim_height = randn(std(height), mean(height), [100, 1]); - [ ] sim_height = randn(mean(height), std(height), [100, 1]); # Which statement returns a cell array of the strings containing '`burger`' from `menu`? `menu = {'hot dog' 'corn dog' 'regular burger' 'cheeseburger' 'veggie burger'}` - [ ] menu{strfind(menu, 'burger')} - [ ] menu(strfind(menu, 'burger')) - [ ] menu{contains(menu, 'burger')} - [x] menu(contains(menu, 'burger')) # What is the set of possible values that `a` may contain? ``` a = randi(10, [1, 10]); a(3) = 11; a(a>2) = 12; ``` - [ ] 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 - [x] 1, 2, 12 - [ ] 2, 11, 12 - [ ] 1, 12 # Which statement is true about the sparse matrices? - [ ] You can use the `sparse` function to remove empty cells from cell array variables. - [x] Sparse matrices always use less memory than their associated full matrices. - [ ] Mixtures of sparse and full matrices can be combined in all of MATLAB's built-in arithmetic operations. - [ ] The `sparse` function requires its input to be a full matrix with at least 50% zero elements. # Which statement using logical indices will result in an error? `a = 1:10;` - [ ] b = a(a ~= 11) - [ ] b = a(a == 1) - [x] b = a(a>6 && a<9) - [ ] b = a(a | 1) # Which statement turns `menu` into the variable `menu_string` below? ``` menu = {'hot dog' 'corn dog' 'regular burger' 'cheeseburger' 'veggie burger'} menu_string = 'hot dog corn dog regular burger cheeseburger veggie burger' ``` - [x] menu_string = cell2mat(join(menu, newline)) - [ ] menu_string = cell2mat(join(menu, '\n')) - [ ] menu_string = join(menu, newline) - [ ] menu_string = cell2mat(pad(menu)) # Which code snippet sets a new random seed based on the current time and saves the current settings of the random number generator? - [x] `rng_settings_curr = rng('shuffle');` - [ ] ``` rng(time()); rng_settings_curr = rng(); ``` - [ ] `rng_settings_curr = rand('shuffle');` - [ ] ``` rng('shuffle'); rng_settings_curr = rng(); ``` # You have a matrix `data` in which each column is mono audio recording from a room in your house. You've noticed that each column has a very different mean and when you plot them all on the same graph, the spread across the y axis make it impossible to see anything. You want to subtract the mean from each column. Which code block will accomplish this? - [ ] `data_nomean = data - repmat(median(data), size(data, 1), 1);` - [x] `data_nomean = bsxfun(@minus, data, mean(data));` - [ ] ``` data_nomean = zeros(size(data)); for i = 1:size(data, 1) data_nomean(i, :) = data(i, :) - mean(data(i, :)); end ``` - [ ] `data_nomean = zscore(data');` # Which code block results in an array `b` containing the mean values of each array within `C`? - [ ] ``` b = zeros(1, size(C, 2)); for i_C = 1:size(C, 2) b(i_C) = mean(C(i_C)); end ``` - [ ] `b = cellfun(@mean, C);` - [ ] ``` b = zeros(1, size(C, 1)); for i_C = 1:size(C, 1) b(i_C) = mean(C{i_C}(:)); end ``` - [x] `b = cellfun(@(m) mean(m(:)), C)` # Which statement creates a logical array that is 1 if the element in `passwords` contains a digit and 0 if it does not? `passwords = {'abcd' '1234' 'qwerty' 'love1'};` - [ ] contains(password, '\d') - [ ] ~isempty(regexp(passwords, '\d')) - [x] cellfun(@(x) ~isempty(regexp(x, '\d')), passwords) - [ ] regexp(passwords, '\d') # Which is NOT a function that adds text to a plot? - [ ] title - [ ] text - [x] label - [ ] legend # Which code block most likely produced this graph?  - [ ] ``` figure x = rand(10,10); r = corrcoef(x); surf(r) colorbar ``` - [x] ``` figure x = rand(10,10); r = corrcoef(x); imagesc(r) colorbar ``` # What kind of files are stored with the .mat extension? - [ ] figure files - [ ] script files - [ ] function files - [x] stored variable files # You would like to randomly reorder every element in array a and put the result into another array b. Which code is NOT necessary to do that? `a = 1:10;` - [x] `b = a(randi(10, 1, 10));` - [ ] ``` m = perms(a); i = randi(factorial(10), 1); b = a(m(i, :)) ``` - [ ] ``` [s, j] = sort(rand(10, 1)); b = a(i); ``` - [ ] ``` b = a(randperm(10)); ``` # Which statement returns **1** (true)? ``` a = 'stand' b = "stand" ``` - [x] a == b - [ ] ischar(b) - [ ] length(a) == length(b) - [ ] class(a) == class(b) # Which does E contain? ``` C = {'dog' 'cat' 'mouse'} D = {'cow' 'piranha' 'mouse'} E = setdiff(C,D) ``` - [x] E = {'cat'} {'dog'} - [ ] E = {'mouse'} - [ ] E = {'cat'} {'cow'} {'dog'} {'piranha'} - [ ] E = # Where in the UI can you see what variables have been created, their values, and their class? - [ ] Editor - [ ] command window - [ ] details - [x] workspace # Given the following x and y coordinates, which choice calculates a linear regression for the x and y coordinates, and which plots the points of the x,y data and the regression line on the same graph? ``` x = 9.0646 6.4362 7.8266 8.3945 5.6135 4.8186 2.8862 10.9311 1.1908 3.2586 y = 15.4357 11.0923 14.1417 14.9506 8.7687 8.0416 5.1662 20.5005 1.0978 ``` - [x] ``` coeff_line = polyfit(x,y,1) x_line = floor(min(x)):0.1:ceil(max(x)); y_line = polyval(coeff_line,x_line) figure; plot(x,y,'o') hold on plot(x_linemy_line) ``` - [ ] ``` figure plot(x,y,'o') coeff_line = polyfit(x,y,1); x_line = floor(min(x)):0.1:ceil(max(x)); y_line = polyval(coeff_line,x_line); plot(x_line,y_line) ``` - [ ] ``` figure plot(x,y) coeff_line = polyfit(x,y,1); x_line = floor(min(x)):0.1:ceil(max(x)); y_line = polyval(coeff_line,x_line); hold on; plot(x_line,y_line) ``` - [ ] ``` coeff_line = polyfit(x,y,1); x_line = floor(min(x)):0.1:ceil(max(x)); y_line = polyval(coeff_line,x_line); figure; plot(x,y,'o') hold on plot(x_line,y_line) ``` # If you run this piece of code, you will get an error. Why? ``` a = [0 1 2 3; 4 5 6 7]; a = a^2; ``` - [x] You are attempting to multiply a non-square matrix by itself, causing a dimension mismatch. - [ ] MATLAB does not allow you to square all the elements in the matrix in a single operation. - [ ] You must use the \*\* operator instead of the ^ operator. - [ ] You cannot square matrices that have a 0 as the first element. # Which command will create a 10-element vector v with values from 1 to 10? - [ ] v = {1:10} - [ ] v = [1-10] - [x] v = 1:10 - [ ] v = (10) # For a 5 x 5 array, the two subscript index (4,2) indexes the same location as linear index `___`. - [ ] 7 - [ ] 8 - [ ] 17 - [x] 9 # What is a difference between global variable and persistent variables? - [ ] Global variables have a higher performance overhead than persistent variables. - [ ] Global variables remain in memory after clear all; persistent variables do not. - [ ] Global variables can be used to cache data in memory; persistent variables cannot. - [x] Global variables are accessible outside the function scope; persistent variables are not. # How is the random seed for MATLAB's random number generator first initializedin a MATLAB Session? - [ ] Seed is undefined until it is initialized by the user. - [ ] Seed is set to a value based on the current time when user first calls rand() - [ ] Seed is set to a value based on the current time on startup. - [x] Seed is set to a static default value on startup. [Reference](https://ch.mathworks.com/help/matlab/math/why-do-random-numbers-repeat-after-startup.html) # At what will MATLAB look first for a called function? - [ ] functions on the path - [ ] built-in functions - [ ] functions within the current file - [x] functions within the current directory [Reference](https://www.mathworks.com/help/matlab/matlab_env/files-and-folders-that-matlab-accesses.html) # Which choice is the correct syntax for declaring a function that returns the input value as the output? - [ ] ``` function mystery_func(a) : return a ``` - [x] ``` function b = mystery_func(a) b = a; end ``` - [ ] ``` def b = mystery_func(a) b = a; end ``` - [ ] ``` function mystery_func(a) b = a; return b; end ``` [Reference](https://mathworks.com/help/matlab/ref/function.html) # What is the state of a at the end of this code? ``` a = [1 2; 3 4]; b = a(:,2); c = b + 3; a(1:2,1) = c; ``` ``` a = 6 3 7 4 ``` - [ ] ``` a = 5 2 7 4 ``` - [x] ``` a = 5 7 ``` - [ ] ``` a = 6 7 ``` - [ ] [Reference](https://mathworks.com/company/newsletters/articles/matrix-indexing-in-matlab.html) # You've just plotted some data and want to change the color behind the lines you've plotted to black. Which code block will accomplish this? - [ ] `h_f = figure; set(h_f,'Color', [0 0 0]);` - [x] `h_a = gca; set(h_a,'Color', [0 0 0]);` - [ ] `h_a = axes; set(h_a,'Color', [0 0 0]);` - [ ] `h_f = gcf; set(h_a,'Color', [0 0 0]);` # Which statement will return all the odd numbers from 1 to 9? - [ ] `2*[1:5]+1` - [x] `1:2:9` - [ ] `isodd(1:9)` - [ ] `1:odd:9` # In MATLAB, the `imfilter` command performs a convolution operation between an image and a matrix. Suppose you have an image loaded in MATLAB into the variable `img` and you apply the following code. The original image appears slightly blurred because the convolution smoothed out the image (removed noise). Why do you think this happened? ``` h = ones(5,5)/25; imshow(imfilter(img,h)); ``` - [ ] `h` is a Gaussian filter that adds to 1. Its intended effect is to highlight image edges. - [x] `h` is an averaging filter uniformly distributed that adds to 1. Its intended effect is to smooth out images (remove noise). - [ ] `h` is a Laplacian filter that adds up to 0. Its intended effect is to smooth out images (remove noise). - [ ] `imfilter` is a function that always blurs the images. # What is the size of `b`? ``` a = [1 2 3]; b = repmat(a,2,3); ``` - [ ] 1x3 - [ ] 3x2 - [ ] 2x3 - [x] 2x9 # Which statement reverses vector `a`? ``` a = [ 1 2 3 4]; ``` - [ ] reverse(a) - [x] a(end:- 1:1) - [ ] rev(a) - [ ] a(::-1) # Which command will create a column vector with the values 7, 8, and 9? - [ ] `c = [7,8,9]` - [ ] `c = [7: 8: 9]` - [x] `c = [7; 8; 9]` - [ ] `c = [7 8 9]` # What do you call in the **command** window to see all the variables in the workspace and their classes? - [ ] `who` - [ ] `vars` - [x] `whos` - [ ] `who all` # You wrote a new function named `snap` in an m-file and when you call it, you're not getting the output you expect. You previously wrote a different function named `snap`, which you think might also be on the search path. Which command can you use to see if the old `snap` function is being called? - [x] which - [ ] who - [ ] lookfor - [ ] what # What is a reason to save a MAT-file using the `-v7.3` flag? - [ ] to ensure backward compatibility - [ ] to avoid HDF5 overhead in MAT-file - [x] to include a variable greater that 2GB - [ ] to use compression by default # Which choice cannot add a directory to the search path? - [ ] the **path** function - [x] the **savepath** function - [ ] using **Set Path** in the **Environment** menu - [ ] the **addpath** function [Reference](https://www.mathworks.com/help/matlab/ref/savepath.html) # Which is not a function to plot three-dimensional data? - [ ] mesh - [ ] surf - [ ] contour - [x] grid [Reference](https://www.mathworks.com/help/matlab/ref/grid.html) # What is the reason to save a MAT-file using the v-7.3 flag? - [ ] to use compression by default - [ ] to ensure backward compatibility - [x] to include a variable greater than 2GB - [ ] to avoid HDF5 overhead in MAT-file [Reference](https://www.mathworks.com/matlabcentral/answers/169755-saving-variable-with-v7-3-flag-check) # This graph could be the result of which block of code?  - [x] `a = randn(1,1000); histogram(a) ylabel('counts')` - [ ] `a = rand(1,1000); histogram(a) ylabel('counts')` - [ ] `a = randi(1,1000); histogram(a) ylabel('counts')` - [ ] `a = rng(1,1000); histogram(a) ylabel('counts')` # What is a key difference between && and &? - [ ] && is a logical operator and & is not. - [ ] && is always slower than & - [x] && employs short-circuiting behavior and & does not. - [ ] && is a bitwise operator and & is not. [Reference](https://stackoverflow.com/questions/1379415/whats-the-difference-between-and-in-matlab) # What is the result of this code? ``` s="abcd"; s(3)='x' ``` - [ ] "abxd" - [ ] abxd - [x] a 1x 3 string array - [ ] a run-time error