MATLAB

Question 1

matlab install direcory?

Answer 1

Type, matlabroot in command window.

Question 2

matlab: three dots … meaning?

Answer 2

Line continuation.

Question 3

matlab: How to measure elapsed time?

Answer 3

using matlab ‘tic’ and ‘toc’.
‘tic’ starts a stopwatch. ‘toc’ gives the elapsed time in seconds.
‘tic’ will reset the stopwatch.

Question 4

How do u find type of a variable in matlab?

Answer 4

class(varName)

— or —

whos your_variable

Question 5

matlab: find dimentions of an array / matrix

Answer 5

size(your_array)
size(your_matrix)

class(your_matrix) gives the type of data elements contained in the matrix.

A column vector has N rows and one column. Dimension N x 1

A row vector has one row and N columns. Dimension 1 x N

whos your_array
gives all info (size, type) of array.

To get total num of elements
numel(your_matrix);

Question 6

How to get info about machine architecture on which matlab is running on?

Answer 6

Type ‘computer’ on command window.

> [str, maxsize, endian] = computer;

Question 7

What does a call to dsp.SineWave(…) return?

Answer 7

A column vector of sine wave samples, containing ‘SamplesPerFrame’ samples.

Question 8

What does randi() function do?

Answer 8

Returns a matrix of random nums, in a given range, in a matrix of given shape.

randi(99, 1, 4): returns a 1x4 array of ints 1 … 99

randi([10, 20], 3, 4): returns a 3x4 matrix of ints 10 … 20

randi([10, 20], 3): returns a 3x3 square matrix of ints 10 … 20

randi([10, 20], ): returns one integer between 10 and 20

randi(range, shape)

Question 9

How to draw scatter plot in matlab?

Answer 9

scatter([1 2 3], [1 4 9]);
scatter([1 2 3], [1, 8, 27], ‘*’, ‘r’)

scatter() needs both X & Y data arrays.
scatterplot() can work with only Y data array, X array is inferred.

Question 10

matlab: How to do “Phase Shift Keying” (PSK) for given baseband data.

Answer 10

Use pskmod()

Question 11

How does cat/concatenate of arrays/matrices work in matlab?

Answer 11

x = cat(dim, arr1, arr2);
dim is the dimension that will increase after matrices are put together.

A row array is of dimension 1xn
To cat two row arrays, dim=2, since num of columns will increase.

Two cat two column vectors, use dim=1, since number of rows will increase.

Question 12

matlab:
x = 23;
what is type of x?

Answer 12

double

This is default of numeric variable.

Question 13

matlab:
How do you create an uint16 type variable?

Answer 13

x = uint16(78);

other variable types are int16, uint8, int32, uint64,
single , double etc.

Question 14

matlab: how to find minim value in an array?

Answer 14

min(array_name);

max is also available.

Question 15

matlab: How to get absolute values of an array X?

Answer 15

y = abs(X);

y will have same dimensions as X, but each element will have absolute value of X elem. No negatives.

Question 16

Matlab: How to find mean of an array X?

Answer 16

If X is a row or column vector,

mean(X) returns mean value.

If X is a matrix,
mean(X) returns an row vector, containing mean of each column.

Question 17

Matlab: How do u open a file?

Answer 17

[fd, err_msg] = fopen(‘abc.data’, ‘r’);

data = fread(fd, inf, ‘int16’);
data will be a row vector of int16.

Question 18

matlab: what is the last element of the array X.

Answer 18

X(end)

Question 19

Give some examples of array slicing in matlab.

Answer 19

X(3 : 7)
X(5 : end)
X(1:2:end) % All odd index elements.

Step size is in the middle.
If the step size is negative, successive indices decrease.

X(end: -1: 1) % Reverse the array.

For matrices
one or both indices can be ranges,
A(2:4, 1:2)

A single : indicates 1:end
A(3,:) % Third row, all cols.

A(: , end) % last column

Question 20

Matlab: What happens when you apply a single index to a matrix?

Answer 20

Matrix is considered a tall column vector.

Question 21

ML: How to find if a variable is number/scalar or an array/matrix?

Answer 21

isscalar(x)

Question 22

Matlab: How to temporarily add a search path in matlab?

Answer 22

addpath(‘/new/path/dir’);

Question 23

Matlab: how to comment out a block of lines?

Answer 23

Enclose block of lines with

%}

Question 24

How to record matlab activity in a file (diary file)

Answer 24

diary abc.txt
disp(‘abc’)
diary off

Question 25

matlab: How to read a CSV file into a matrix?

Answer 25

readmatrix(‘file_name.csv’);

Question 26

Matlab: what is difference between single quoted characters and double quoted characters?

Answer 26

Single quoted characters create a ‘character array’.

Double quoted characters create strings.

Question 27

Matlab: how to do u create tables?

Answer 27

Use function ‘table’. Provide it with column arrays of same sizes.

T = table(name_vec, age_vec);

Table column names are same as input vector names.

height(T) returns the number of rows in table

Question 28

Matlab: How different columns of a table can be accessed?

Answer 28

If column name or variable name is a string without spaces,
tbl.varName

if column name contains spaces,
tbl.(‘var name’);

Question 29

Matlab: Undo ?

Answer 29

CTL + Shift + minus

Question 30

Matlab: How to append at the end of an arry?

Answer 30

array name = arr

For row vector,
arr = [arr, new_val]

For column vector,
arr = [arr ; new_val]

Question 31

Matlab: Duplicate a line?

Answer 31

CTL + SHIFT + c

Question 32

Matlab: How to suppress the output of a command to console?

Answer 32

use evalc,
evalc(‘ command here ‘);
remember to use quotes around command.

evalc(‘fprintf(‘‘Hello, World!’’)’);

Question 33

Matlab: Can you add fields to structs dynamically, while program is running?

Answer 33

yes,

sruct.new_field = new_val;

Question 34

Matlab: how to make sure a specific struct indeed has a specific field?

Answer 34

isfield(struct_name, field_name)

Question 35

Matlab: How to create a struct with given set of field, field_value pairs?

Answer 35

x = struct(‘field_name1, field-val_1, field_name2, field_val_2, …)

Question 36

Matlab: What is ‘nargin’?

Answer 36

Inside a function, it is the number actual number of arguments that the function is called with.

Question 37

Matlab: What is ‘varargin’?

Answer 37

Inside a function, it is a cell array containing all arguments passed to the function.

Question 38

Matlab: What is function handle?

Answer 38

It is a variable containing a function name.
Function can be called using this variable.

fh = @function_name

call the function
fh(a, b, c)

Question 39

Matlab: What does deal function do?

Answer 39

It distributes all of its input arguments to receiver arguments,

eg,

[a, b] = deal(7, 10);

Useful in initializing cell arrays with known values.

Question 40

matlab: How does max() work on an array.

Answer 40

[a, b] = max(arr)

a = max value
b = index of max value

Question 41

matlab: What are sub functions and nested functions?

Answer 41

Sub-function is a func defined in a a .m file after the definition of the main function. Sub-func is invisible outside its .m file.

Nested func is defined inside the body of a function.

Question 42

matlab: What are ways to print error/warning messages?

Answer 42

error(“Error message”)
Halts the program.

warning(“Warning message”);
Does not halt the program. Prints line number automatically.

Question 43

matlab: how to get documentation and help about a function, object, class?

Answer 43

On command line, type

doc mean

help median

Question 44

matlab: How to get information about a table (tbl)?

Answer 44

tbl.Properties
tbl.Properties.VariableNames
height(tbl)

Question 45

matlab: How do you define a class?

Answer 45

Using ‘classdef’

With sections
properties
methods

Question 46

Matlab: How to list properties of a class?

Answer 46

properties(class_name);

Question 47

Matlab: How to find all methods of a class?

Answer 47

methods(class_name);
methodsview(class_name);

Question 48

Matlab: How to get total num of elements in a array or matrix?

Answer 48

numel(mtx_name);
numel(array_name);

size(mtx_name) gives dimensions.