matlab

Question 1

to know the size of a matrix

Answer 1

size(the name of the variable)

Question 2

to call out a certain number in the matrix

Answer 2

variable name(row number,column number)
x(3,1)

Question 3

to call out an entire row in a matrix

Answer 3

using :
x(3,:) is calling out row 3 , nafs l klam m3a l column

Question 4

dot multiplication between two matrix bytala3 scalar

Answer 4

dot(x,y)

Question 5

cross product between two vectors

Answer 5

cross(x,y)

Question 6

the constant e

Answer 6

exp(1)

Question 7

zero or ONE matrix with diff rows and columns

Answer 7

zeros(rows,columns)
ones(rows,columns)

Question 8

determinant of a matrix

Answer 8

det(A)

Question 9

to display a value or a variable

Answer 9

disp(A)
disp(‘ i found it ‘ )

Question 10

for loop

Answer 10

for i=1:10
ekteb ele anta 3awzo
end

Question 11

to plot
to enter a title
to label x and y axis
sub plot

Answer 11

plot(x,y)
title(‘A plot of sin x ‘) 3la sbeel el msaal
xlabel(‘time’) ylabel(‘3afreet’)
subplot(2,1,1)
plot m4 3aref eh
subplot(2,1,2)plot 7aga tanya

Question 12

3adad el steps mabeen value and another value

Answer 12

x=linspace(0,100,200)
hy3ed mn 0 l 100 f 200 step

Question 13

to plot 2 graphs 2 xs and 2 ys on the same graph

Answer 13

plot(x,y,x,y_2)
plot(x,y,’–‘,x,y_2,’.’)
hyrsem l graph l 2awalany f dashes wel tany f no2at

Question 14

bar chart

Answer 14

bar(x)
bar(x,y) hyrsemlak bars :D

Question 15

pie chart

Answer 15

pie(x)

Question 16

scatter chart used lama l data m4 ordered kwyes

Answer 16

scatter(x,y)

Question 17

3d plotting of a matrix

Answer 17

surf(z)
contour(z)

Question 18

to read wave files ( any file that contains digital sound recorded for example by Audicity )to check the size of the matrix

Answer 18

d=wavread(‘ Filename.wav’); or u can use audioread(‘Filename.mp3 or wav ‘ )
size(d)

Question 19

to let matlab say outloud the wave file u recorded

Answer 19

[d,fs]=wavread(‘Filename.wav’);sound(d,fs);
NB: d is the variable name, fs is frequency sampling

Question 20

to reverse a sound signal and audiowrite it in a new mp3 file

Answer 20

d2=flipud(d);
d3=audiowrite(‘helloworldreversed.mp4’, d2, fs);
[d3,fs]= audioread(‘helloworldreversed.mp4’);
sound(d3,fs)

Question 21

to speed up the sound

Answer 21

d4=downsample(d,2);
is like doubling the frequency of a wave..

Question 22

to draw the FFT “ fast fourier transform “ which is aka frequency spectrum .. u can also draw only the real part of the signal ( while ignoring the imaginary part )

Answer 22

y=fft(d);
z=real(y);
plot(z)

Question 23

spectogram shows different frequencies with change of time. u need to have a tool box from MATLAB company to use it.

Answer 23

spectogram(y2)

Question 24

applying a low pass filter an audio stream
dlp is the low passed audio

Answer 24

b=ones(40,1)/4;
[d.fs]=audioread(‘Helloworld.mp3’);
dlp=filter(b, 1, d);
sound(‘dlp’)

Question 25

to read an image in matlabto show an image

Answer 25

A=imread(‘lena.bmp’);
imshow(A)

Question 26

to flip an image upsideto flip an image horizontally..

Answer 26

u=flipud(A);
u=fliplr(A);

Question 27

any image has only 3 colour channels . Red , green and blue
so to show only the colour blue in a picture u gotta disable red and green which are the first two channels.

Answer 27

B=image;
B(:, :, 1)=0;
B(:, :, 2)=0;
imshow(B) > gonna be blue

Question 28

to blur an image using a Gausian filter

Answer 28

H=fspecial(‘gaussian’, 25, 5);
c=conv2(double(A(:, :, 1)), h/1000) ;
should go lower than 1000
imshow(c)
the real gaussian filter looks like imshow(h/max(max(h))

Question 29

to see everything clearly and sharply with no colours.

Answer 29

E=edge(A(:,:,1));
imshow(E)

Question 30

to generate random numbers

Answer 30

R= randi(10) ; will generate a random number below 10
R= randi(10,3); will generate a random matrix 10 rows, 3 columns

Question 31

to get the mean value of a given data

Answer 31

mean(R)

Question 32

to get the variance of given numbers from the average

Answer 32

var(R)

Question 33

Try displaying more decimal places of the variable x

Answer 33

format long
x
and to go back u need to type
format short
x

Question 34

starts at 1, ends at 5, with each element separated by 0.5

Answer 34

z=1:0.5:5

Question 35

starts at 1, ends at 10, and contains 5 elements

Answer 35

b = linspace(1,10,5)

Question 36

Transpose b from a row vector to a column vector

Answer 36

b=b’

Question 37

create a column vector named c that starts at 5, ends at 9, and has elements that are spaced by 2.

Answer 37

c = (5:2:9)’

Question 38

Extract the value in the last row and 3rd column of the variable data

Answer 38

y=data(end,3)
or end-1 xD

Question 39

performs element-wise multiplication by multiplying the corresponding elements of two equally sized arrays.

Answer 39

.*
z = [3 4] .* [10 20]