Intro 1/2

Question 1

Get description of function

Answer 1

help + function

Question 2

hide response

Answer 2

use semicolon
;

Question 3

print something

Answer 3

disp(“hello”)
A=10;
disp(A)

Question 4

Make the format tighter

Answer 4

format compact

Question 5

Get information about a specific variable

Answer 5

Example:
var1 = [1,2,3,4];
whos (“var1”)

It lists all the variables in the current workspace, together with information about their size, bytes, class, etc.

–> Output

Name Size Bytes Class Attributes

var1 1x4 32 double

Question 6

example of scalar (zero-dimentional)

Answer 6

A=9

Question 7

make a row vector

Answer 7

my_rowvector = [5 4 12 10 8]

Question 8

make a column vector

Answer 8

my_columnvector = [1; 2; 14; 5; 6]

Question 9

Make a matrix

Answer 9

M = [1, 23, 15; 6, 7, 11; 0, 16, 8]

Question 10

construct special, equally spaced vector (with and without specifying step size)

Answer 10

without step size –> E = 5:10

with step size –> F = 0.25:0.5:2 or G = 10:-2:0 or tryout = 1:-0.1:-1

Question 11

Combine smaller arrays into a larger one (rectangular shape). Create a matrix F from C = [1, 2, 3; 4, 5, 6], D = [7; 8], and E = [9, 0].

Answer 11

C = [1, 2, 3; 4, 5, 6];
D = [7; 8];
E = [9, 0];
F = [C, D; E, E];

Question 12

Add a new row [1, 15, 18] to an existing matrix M

Answer 12

M_addition = [1, 15, 18];
M_new = [M; M_addition];

Question 13

Extract the value in row 4, column 3 of a magic(5) matrix assigned to A.

Answer 13

A = magic(5);
value = A(4, 3);

Question 14

Extract rows 1, 3, and 5 and columns 2 and 4 from a matrix A.

Answer 14

submatrix = A([1, 3, 5], [2, 4]);

Question 15

Extract the four values in the bottom right corner of a matrix A.

Answer 15

bottom_corner = A([4, 5], [4, 5]);

Question 16

Extract the central 3x3 submatrix from A.

Answer 16

central_submatrix = A(2:4, 2:4);

Question 17

Extract all rows of the first column and the last three rows of matrix A.

Answer 17

first_column = A(:, 1);
last_three_rows = A(3:5, :);

Question 18

Change values in a matrix A:

Set A(4,4) to 10.
Change row 2, columns 1 to 3 to 5.
Set all values in column 4 to 0.

Answer 18

A(4,4) = 10;
A(2,1:3) = 5;
A(:,4) = 0;

Question 19

Add a new column [1, 5, 10, 16, 7] and a new row [6, 7, 80, 9, 3, 5] to matrix A.

Answer 19

new_column = [1; 5; 10; 16; 7];
A(:,6) = new_column;

new_row = [6, 7, 80, 9, 3, 5];
A(6,:) = new_row;

Question 20

Create matrices a and b, and form f (stacked vertically) and g (specific columns).

Answer 20

a = [9, 12, 13, 0; 10, 3, 6, 15; 2, 5, 10, 3];
b = [1, 4, 2, 11; 9, 8, 16, 7; 12, 5, 0, 3];

f = [a; b];
g = [a(:,1), b(:,4)];

Question 21

Modify matrices:

Set e(2,2) to 20.
Set row 1 of a to all zeros.
Set column 3 of f to numbers 1 through 6.
Replace column 1 of a with column 2 of b.

Answer 21

e(2,2) = 20;
a(1,:) = 0;
f(:,3) = 1:6;
a(:,1) = b(:,2);

Question 22

Find the dimensions of a matrix A.

Answer 22

dimensions = size(A);

Question 23

Perform scalar addition, subtraction, multiplication, and power operations.

Answer 23

Use +, -, *, /, and ^. Example:

matlab
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result = 2 + 3; % Addition
result = 4^2; % Power

Question 24

When can matrices be added or subtracted?

Answer 24

Matrices can only be added or subtracted if they have the same size.

Example:

A = [1, 2; 3, 4];
B = [5, 6; 7, 8];
C = A + B; % Matrix addition

Question 25

Perform element-wise multiplication, division, and power.

Answer 25

Use .*, ./, and .^ Example: A = [1, 2; 3, 4]; B = [5, 6; 7, 8]; C = A .* B; % Element-wise multiplication D = A ./ B; % Element-wise division E = A .^ 2; % Element-wise power

Question 26

What is required for matrix multiplication (*)?

Answer 26

The number of columns in the first matrix must equal the number of rows in the second. Example: A = [1, 2; 3, 4]; B = [5, 6; 7, 8]; C = A * B; % Matrix multiplication

Question 27

How do you compute the transpose of a matrix?

Answer 27

Use the ' operator. Example: A = [1, 2; 3, 4]; A_transposed = A'; % Transpose of A

Question 28

Combine matrices vertically and horizontally.

Answer 28

Use square brackets. Example: A = [1, 2; 3, 4]; B = [5, 6; 7, 8]; C = [A; B]; % Vertical stacking D = [A, B]; % Horizontal stacking

Question 29

Perform scalar operations with matrices.

Answer 29

Scalars operate element-wise without needing dots. Example: A = [1, 2; 3, 4]; C = 2 * A; % Scalar multiplication D = A / 2; % Scalar division

Question 30

Why do A*A' and A'*A always work, but not A*A?

Answer 30

A*A' and A'*A have compatible dimensions since the rows and columns align after transposing.

Question 31

Use basic functions like sum, mean, std, max, and min.

Answer 31

Example usage: A = [1, 2; 3, 4]; sum(A, 1); % Column-wise sum mean(A(:)); % Mean of all elements max(A, [], 2); % Row-wise max

Question 32

Create matrices with zeros, ones, rand, randn, etc.

Answer 32

Z = zeros(3, 4); % 3x4 matrix of zeros O = ones(3, 4); % 3x4 matrix of ones R = rand(3, 4); % 3x4 matrix of random numbers

Question 33

Modify and query rows and columns of a matrix.

Answer 33

A = [1, 2; 3, 4]; A(:, 1) = [5; 6]; % Change first column sum(A(2, :)); % Sum of the second row

Question 34

What is the difference between .* and *?

Answer 34

.* multiplies elements in the same positions. * performs matrix multiplication. Example: A = [1, 2; 3, 4]; B = [5, 6; 7, 8]; C1 = A .* B; % Element-wise C2 = A * B; % Matrix product

Question 35

Use scalars with matrix operations.

Answer 35

Scalars operate element-wise. Example: A = [1, 2; 3, 4]; C = 2 .* A; % Scalar multiplication (dot optional) D = A / 2; % Scalar division

Question 36

Perform the following: Add the sum of the first column of A to the second column of B. Compute the mean of all elements in B.

Answer 36

P = sum(A(:, 1)) + sum(B(:, 2)); % Combine column sums mean_B = mean(B(:)); % Mean of all elements

Question 37

Modify matrices (e.g., scale a column, add a row).

Answer 37

A(:, 3) = 3 * A(:, 3); % Scale the third column A(3, :) = [5, 6, 7]; % Add a new row