Page 823 - Mechatronics with Experiments

®
®
MATLAB , SIMULINK , STATEFLOW, AND AUTO-CODE GENERATION 809
®
The main data structure in MATLAB is a “matrix.” A scalar is considered a 1x1
®
matrix. A vector is considered a row matrix. MATLAB does not require the data type of
a variable or matrix be declared. By default, all numerical data is treated as double.
The percent sign, %, is used to indicate the beginning of comments. The semi column
“ ; ” at the end of a line suppresses the echo of the data to the screen. Three dots are used
to indicate that the command line continues in the next line.
Variable names must start with a character, and are case sensitive, so x and X are
different variable names.
Help on any topic can be obtained by

>> help
>> help topic

The display accuracy of the numerical data can be controlled by

>> format short ;
>> format long ;
>> format short e ; % to display in scientific notation
>> format long e ;
>> format bank ; % Display two decimals only, i.e. 5.40
>> format rat ; % Display in fractional form, i.e. 10/3
Matrix data is defined as follows,

>> A = [ 1 2 3
4 5 6
7 8 9 ] ;
The same matrix, A, can also be defined with the following syntax,

>> A = [ 1 2 3 ; 4 5 6 ; 7 8 9 ] ;

Instead of spaces between matrix elements, comma “,” can be used,
>> A = [ 1,2,3 ; 4,5,6 ; 7,8,9] ;

A specific element of a matrix, (k,l) - row k, column l, is referenced as,

>> x = A(k,l) ;
>> A(k,l) = 5.0 ;
>>

A row, or a column or a sub-matrix of a matrix can be referenced (for reading and writing)
>> row_k = A(k, : ) ;
>> col_l = A(:, l ) ;
>> B = A(1:k, 10:20) ; % B is a sub-matrix of A.
√
Note that MATLAB ® uses variable names “i” and “j” for representing −1 imaginary
number for complex variable definitions. In order to make sure we do not change the
definition of built in variables “i” and “j”, we should not use “i” and “j” in our programs as
data variables, such as index number to vectors and matrices. When a “clear” statement is
executed, the original definitions of the variables are restored.

>> clear
>> i