Basics
| Site: | MSubbu Academy |
| Course: | MATLAB for Chemical Engineers |
| Book: | Basics |
| Printed by: | Guest user |
| Date: | Sunday, 17 November 2024, 2:22 PM |
1. Arithmetic Operations
The list of basic arithmetic operations in MATLAB includes six operations:
+ : addition
- : subtraction
* : multiplication
/ : right division
\ : left division
^ : power
2. Simple Math
One can use MATLAB like a calculator without specifying variables. MATLAB has all the standard mathematical operations.
>> 2+2.5+106
ans = 110.5000 >> 4*25 + 2^3 ans = 108
3. MATLAB Variables
>> D = 2 D = 2 >> v = 3 v = 3
To recall the variable use arrow keys up ↑ and down ↓ for scrolling through previous commands.
>> D D = 2 >> >> rho = 1000; >> mu = 0.001; >> Re = D*v*rho/mu Re = 6000000 >>
MATLAB does not require any type declarations or dimension statements. MATLAB is case sensitive; it distinguishes between uppercase and lowercase letters. The variables "A" and "a" are not the same variable. Variable name can contain up to 63 characters. Variable names start with a letter, followed by letters, numbers or underscores. (e.g.: NRe_2_the_power2by3)
4. M files
In addition to executing commands entered through the keyboard, you can also use commands stored as files. These files all end in the extension .m and are called M-files because of the file name extension. Long programs are usually created in a text editor and stored as an M-file that can be executed in a MATLAB session. Short programs are usually created and run directly on-line.
M files are of two types: script m file and function m file. Function m file starts with the keyword function.
5. Script M file
A script file is an external file that contains a sequence of MATLAB statements. By typing the filename, subsequent MATLAB input is obtained from the file.
% frictionfactor.m
% Done on 16-Dec-2001
% Re-Done on 28-Jan-2011
D = input('Dia in meter = ');
v = input('Velocity in m/s = ');
rho = 1000; % Density of water in kg/m3
mu = 0.001; % Viscosity of water in kg/m.s
Re = D*v*rho/mu
f = 0.079*Re^(-0.25);
disp(f);
>> frictionfactor Dia in meter = .1 Velocity in m/s = 2 Re = 200000 0.0037
6. List of Variables in the Workspace
The command who is used to get to know the variables in the current workspace.>> who
Your variables are:
D Re mu rho v ans
>>
7. Clearing Variables
>> clear D >> who Your variables are: NRe ans mu rho v >> >> clear >> who >>
clear variable1, variable2... will clear the variables specified.
8. Equally Spaced Arrays
Typing every entry is time consuming for long arrays. If the points are equally spaced this isn't necessary. An alternative method is to use the colon notation [first_value : interval : last_value]>> a = 1:2:10
a =
1 3 5 7 9
>>
Another way of specifying an equally-spaced array is to use the linspace command. This allows you to specify the number of data points, but not the interval to be used. The notation is:
linspace(first_value, last_value, number_of_values)
If the data for number_of_values is not specified, it is taken as 100.
9. Semicolon
The semicolon (;) can be used to end rows of vectors or matrices. It is used very often, however, to suppress the displaying of the variable in the command window. The semicolon can also be used to separate statements on the same line such as:>> Num_of_Students=50; Num_of_Teachers=12;
10. Colon
The colon(:) is one of the most useful operators in MATLAB. It can create vectors, subscripts, and specify for loop iterations. The colon operator uses the following rules to create regularly spaced vectors: j:k is the same as [j,j+1,...,k] Below are the definitions that govern the use of the colon to pick out selected rows, columns, and elements of vectors, matrices, and higher-dimensional arrays:A(:,j) is the j-th column of A
A(i,:) is the i-th row of A
11. Array Addressing
>> x = 1:10; >> y = sin(x) y = Columns 1 through 7 0.8415 0.9093 0.1411 -0.7568 -0.9589 -0.2794 0.6570 Columns 8 through 10 0.9894 0.4121 -0.5440 >> >> y(3) ans = 0.1411 >> y(1:5) ans = 0.8415 0.9093 0.1411 -0.7568 -0.9589 >>
12. Relational Operators
| A < B | Less than |
| A > B | Greater than |
| A <= B | Less than or equal |
| A >= B | Greater than or equal |
| A == B | Equal |
| A ~= B | Not equal |
13. Logical Operators
| & | a < b & b >= c |
| | | or |
| ~ | not |
13.1. Example
% Ex_LogicalOperators.m
% Re <= 2100 laminar
% Re >= 4000 Turbulent
% 2100 < Re < 4000 transition
Re = input('Reynolds Number = ');
if Re <= 2100
disp('Laminar');
elseif Re< 4000
disp('Transition');
else
disp('Turbulent');
end
if Re > 2100 && Re < 4000
disp('Modify the flow conditions please,')
disp('as the flow regime is uncertain')
end
14. Matrix
We can input a matrix elements by leaving a space between elements, or separating the elements with a comma as below. We can end a row by typing the elements in the next row by pressing enter key. Row can also be ended by using semicolon.>> A = [1 2 -2
2 -1 0]
A =
1 2 -2
2 -1 0
>> A = [1,2,-2
2,-1,0]
A =
1 2 -2
2 -1 0
>> A = [1 2 -2; 2 -1 0]
A =
1 2 -2
2 -1 0