matlab week 2.1

Question 1

what should you do to matrices to properly store data?

Answer 1

transpose

Question 2

: operator in indexing (i.e (2, :))

Answer 2

serves as ‘select all’ and allows you to select specific rows or columns

Question 3

to a computer everything is ____

Answer 3

numbers.

Question 4

ASCII

Answer 4

system that stores letters and special characters as number for computer

Question 5

uint(‘a’)

Answer 5

returns ASCII number, in this case 97

Question 6

char( 97 )

Answer 6

returns character that ASCII number represents, in this case a

Question 7

num2str()

Answer 7

converts numbers to string with ASCII represented characters

Question 8

str2num()

Answer 8

converts string to ASCII number representation

Question 9

adding a number to a string…

Answer 9

just concatenates with ASCII rep of number, doesn’t do what you want

Question 10

dimensions of array being concatenated must be…

Answer 10

the same

Question 11

multidimensional matrix

Answer 11

third layer that allows multiple ‘pages’ in a book of code

Question 12

find(x)

Answer 12

if you have an array x

locates all nonzero elements of array x and outputes the corresponding indices in x

Question 13

find (X, k, ‘first’)

Answer 13

returns the first k indices corresponding to nonzero elements of the array
-> you can do the same with ‘last’ and it will return first k indices from the back

Question 14

[row, column] = find(B)

Answer 14

finds indies of multidimensional matrix B that are nonzero and stores corresponding row numbers in variable row and column number in variable column

you can add optional ‘v’ to the outputs and that will return what the nonzero numbers are

Question 15

what if X is a logical expression?
[row, col, v] = find( A == 9)

Answer 15

vector v is then logical and will contain the nonzero elements of logical array obtained by evaluating X

Question 16

min function

Answer 16

returns smallest element in vectors, and smallest of each COLUMN in matrices

Question 17

[M, I] = min(A)

Answer 17

returns indices corresponding to a minimum
M is min of each column
I is their indices (row number)

Question 18

M = min(X, [], DIM)

Answer 18

finds minimum along dimension dim
1 means from each column
2 means from each row

Question 19

max function

Answer 19

similar format as min function but finds the largest values of a matrix

Question 20

mean function

Answer 20

takes average value of elements for vector, for matrices it takes the average for each column and returns row vector

Question 21

sum function

Answer 21

takes the sum of all elements for vectors and returns vector with sum for each column for matrices

Question 22

sort function

Answer 22

reorganizes data, default is smallest to largest but to reverse add ‘descend’

Question 23

sortrows function

Answer 23

sorts rows based on specified column
ex:
sortrows(X, 1)
sorts rows of matrix X based on first column

Question 24

input(‘prompt’) vs input(‘prompt’, ‘s’)

Answer 24

adding ‘s’ takes user input in as a string

Question 25

disp function

Answer 25

displays text and variables into the command window