Introduction to MATLAB - Intro to Computer Programming - Lecture Slides, Slides of Computer Engineering and Programming

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Introduction to MATLAB

Lecture 18

MATLAB

• MATLAB is a program for doing numerical computation. It was originally designed for solving linear algebra type problems using matrices. It’s name is derived from MATrix LABoratory.
• MATLAB has since been expanded and now has built-in functions for solving problems requiring data analysis, signal processing, optimization, and several other types of scientific computations. It also contains functions for 2-D and 3-D graphics and animation.

MATLAB

To get started, type one of these commands: helpwin, helpdesk, or demo

EDU» a=5;

EDU» b=a/

b =

EDU»

MATLAB Variable Names

• Variable names ARE case sensitive
• Variable names can contain up to 63 characters (as of MATLAB 6. and newer)
• Variable names must start with a letter followed by letters, digits, and underscores.

MATLAB Math & Assignment Operators

Power ^ or .^ a^b or a.^b

Multiplication * or .* ab or a.b

Division / or ./ a/b or a./b

or \ or .\ b\a or b.\a NOTE: 56/8 = 8\

• (unary) + (unary)

Addition + a + b

Subtraction - a - b

Assignment = a = b (assign b to a)

Other MATLAB symbols

prompt

... continue statement on next line , separate statements and data % start comment which ends at end of line ; (1) suppress output (2) used as a row separator in a matrix

: specify range

MATLAB Matrices

• A matrix with only one row AND one column is a scalar. A scalar can be created in MATLAB as follows:

EDU» a_value=

a_value =

MATLAB Matrices

• A matrix with only one row is called a row vector. A row vector can be created in MATLAB as follows (note the commas):

EDU» rowvec = [12 , 14 , 63]

rowvec =

MATLAB Matrices

• A matrix can be created in MATLAB as follows (note the commas AND semicolons):

EDU» matrix = [1 , 2 , 3 ; 4 , 5 ,6 ; 7 , 8 , 9]

matrix =

Extracting a Sub-Matrix

• A portion of a matrix can be extracted and stored in a smaller matrix by specifying the names of both matrices and the rows and columns to extract. The syntax is:

sub_matrix = matrix ( r1 : r2 , c1 : c2 ) ;

where r1 and r2 specify the beginning and ending rows and c1 and c specify the beginning and ending columns to be extracted to make the new matrix.

MATLAB Matrices

• A row vector can be extracted from a matrix. As an example we create a matrix below:

EDU» matrix=[1,2,3;4,5,6;7,8,9]

matrix =

1 2 3 4 5 6 7 8 9

• Here we extract row 2 of the matrix and make a row vector. Note that the 2: specifies the second row and the 1:3 specifies which columns of the row.

EDU» rowvec=matrix(2 : 2 , 1 : 3)

rowvec =

4 5 6

Reading Data from files

• MATLAB supports reading an entire file and creating a matrix of the data with one statement.

load mydata.dat; % load s file into matrix.

% The matrix may be a scalar, a vector, or a

% matrix with multiple rows and columns. The

% matrix will be named mydata.

size (mydata) % size will return the number

% of rows and number of % columns in the matrix

length (myvector) % length will return the total

% no. of elements in myvector

Plotting with MATLAB

• There are commands in MATLAB to "annotate" a plot to put on axis labels, titles, and legends. For example:

% To put a label on the axes we would use: xlabel ('X-axis label') ylabel ('Y-axis label')

% To put a title on the plot, we would use: title ('Title of my plot')

Plotting with MATLAB

• Vectors may be extracted from matrices. Normally, we wish to plot one column vs. another. If we have a matrix “mydata” with two columns, we can obtain the columns as a vectors with the assignments as follows:

first_vector = mydata ( : , 1) ; % First column

second_vector = mydata ( : , 2) ; % Second one

% and we can plot the data

plot ( first_vector , second_vector )