MATLAB The first steps. Edited by Péter Vass

Transcription

1 MATLAB The first steps Edited by Péter Vass

2 MATLAB The name MATLAB is derived from the expression MATrix LABoratory. It is used for the identification of a software and a programming language. As a software, it provides an interactive computational and program development environment which supports its own programming language. It is a commercial software (not free and not cheap) and developed by the MathWorks Inc.

3 The basic features of MATLAB programming language It is a 4GL programming language, an interpreted programming language (the interpreter is built in the software), a domain-specific programming language (it is aimed at solving scientific and engineering problems). It supports the imperative, the structural, the procedural and the object-oriented programming. It has sophisticated data structures. It provides vast number of built-in functions for linear algebra, statistics, Fourier analysis, filtering, optimization, numerical integration and solving ordinary differential equations.

4 The basic features of MATLAB programming language These functions are collected in packages referred to as toolboxes. It provides built-in graphics for visualizing data, enables the user to create applications with graphical user interface (GUI), and also provides interfaces for programs or functions written in other languages such as C, C++, Java, and FORTRAN.

5 Matlab Integrated Development Environment (IDE) Launching the MATLAB IDE double-clicking the MATLAB shortcut on the desktop, or find the MATLAB item and click it in the start menu Panels of the MATLAB desktop (in the default layout) Current Folder Command Window Workspace Command History

6 Matlab Integrated Development Environment (IDE) Current Folder Workspace Command Window Command History

7 Matlab Integrated Development Environment (IDE) Current Folder allows us to view, open, search for folders and files, and make changes to them. Command Window provides the command prompt (>>) which indicates the position of the command line. The command to be executed must be entered here. The entered command is sent to the interpreter which tries to execute it. If the command is incorrect or some condition is not fulfilled, the interpreter sends an error message which is also displayed in this window.

8 Matlab Integrated Development Environment (IDE) Command Window Otherwise, it executes the command and the result appears in the window. The commands previously entered and the results are listed in sequence above the command line. Workspace shows some information about the variables previously created and/or read from files. Command History lists the commands previously entered in the Command Window. Any command may be recall from here and rerun in the command line by double-clicking it.

9 Matlab Integrated Development Environment (IDE) Customizing the environment Home tab Environment section Preferences

10 Matlab Integrated Development Environment (IDE) Invoking the MATLAB help browser Home tab Resources section Help icon

11 Matlab Integrated Development Environment (IDE) From the command line Type doc in the command line and press the enter key ( ). >> doc Getting information about a valid function >> help funtion_name >> doc function_name Example: >> help exit >> help quit >> doc clc >> clc Watch the content of the Command History window. >> exit

12 Matlab Integrated Development Environment (IDE) Searching help entries for all MATLAB commands linked up with a keyword >> lookfor keyword Example: >> lookfor spectrum There are different levels of working with the MATLAB environment: using it as a high-performance, complex calculator by typing and running commands one after another, writing a script which contains a series of commands arranged in suitable control structures, and is stored in a script file, then running it as a single command, writing user-defined functions for specific tasks and calling them in the command line.

13 Using MATLAB as a calculator In the simplest case, we use only numerical constants in our computation. The symbols used for the notation of basic mathematical operations (operators): + * / ^ To modify the order of operations, use ( ) Example: >> (4 + 2) / 3 The result of an executed command is stored in a special variable named ans (answer). See the content of the Workspace panel. Example: >> ans^2 Note that the value of ans has changed in the Workspace panel.

14 Using MATLAB as a calculator Other special variables for mathematical symbols: pi Inf i and j 1 (imaginary unit) Nan not a number Examples: >> pi >> -2.5/0 >> (-3) ^ 0.5 >> 2+3j * -(5+6j) >> 0/0

15 Using MATLAB as a calculator Setting the output format The default output format is the short format which displays numbers with four decimal place values. By means of the format command, the output format may be changed. Some other output format: long format displays 15 digits after the decimal point, bank format rounds numbers to two decimal places (for finantial computation), format short e displays numbers in exponential form with a base of four decimal places and the exponent, format long e displays numbers in exponential form with a base of 15 decimal places and the exponent

16 Using MATLAB as a calculator Example: >> 3 + 4/3 6^2.3 >> format long >> ans >> format bank >> ans >> format short e >> ans >> format long e >> ans >> format short >> ans

17 Using MATLAB as a calculator Editing the command line There are some useful keyboard shortcut for editing the command line such as: Esc Ctrl Ctrl recalls the previous command recalls the next command clears the command line moves the cursor one character backward moves the cursor one character forward moves the cursor one word to the left moves the cursor one word to the right

18 Using MATLAB as a calculator Editing the command line Home, End, Del and Backspace keys may also be used with their well-known functions. Variables In order to perform more complex computations, we must apply variables in our commands. A variable is a storage location in the memory which serves for keeping the value of some data, and it has an individual name. We can assign a value to it, and use its value in expressions. A variable has three main properties: its name, its type, and its value.

19 Using MATLAB as a calculator Variable assignment variable_name = value or expression Expression is a combination of different elements. It may contain: constants, variables, operators (symbols for the operations), and function calls. Examples >>x = 5 See the content of the Workspace panel. >>x = x + 2 >>y = 2*x sin(pi/4) sin() is a built-in function for implementing the mathematical sine function in MATLAB >>help sin

20 Using MATLAB as a calculator An important rule The variable assignment always has to precede the first use of the variable in a computation. So, a variable without any value cannot be used in an expression. Example >>x = 3 >>x = x + z Since the variable z has not a definite value, the expression in the last command is wrong. MATLAB cannot execute it and we get an error message.

21 Using MATLAB as a calculator Semicolon in MATLAB It may used at the end of the commands. If we use it, MATLAB will not display the output of the executed command. Example >>x = 3; >>y = x + 5 Multiple variable assignments It is possible to perform more than one variable assignment in the same command line in the following way: >> x = 3.4; y = 7.2; z = x * y

22 Using MATLAB as a calculator Naming rules of variables a variable name may contain only letters, numbers and underscore characters, the first character must be a letter, since MATLAB is case-sensitive, the capital and small forms of a letter are differentiated, although there is no limit for the length of a variable name, still only a limited number of characters from the beginning are taken into account (run the function namelengthmax). Example >>varname=5; >>VarName=8; >>varname+varname >>namelengthmax

23 Using MATLAB as a calculator Variable types MATLAB automatically determines the type of a variable whenever we assign a value or expression to it. So, we need not declare the type of any variable unlike other programming languages such as C, Pascal, Fortran, Java etc. Clear command The variables we have created during a MATLAB session are stored in the memory of the computer. It may be necessary to free some memory by erasing useless variables. Erasing variable x from the memory. >>clear x Erasing all the variable from the memory >>clear

24 MATLAB clones MATLAB is an excellent software but it is not free and not cheap. This is the reason why someone may consider trying out a free alternative of MATLAB. There are some free MATLAB clones or MATLAB-like applications such as: GNU Octave, SciLab and Rlab. The home page of Octave: The home page of Scilab: The home page of Rlab: Octave is the most compatible with MATLAB of all the clones.

25 Octave MATLAB is an excellent software but it is not free and not cheap. This is the reason why someone may consider trying out a free alternative of MATLAB. There are some free MATLAB clones or MATLAB-like software such as: GNU Octave, SciLab and Rlab. The home page of Octave: The home page of Scilab: The home page of Rlab: Octave is the most compatible with MATLAB of all the clones.

26 Graphical User Interface (GUI) of Octave Launching Octave double-click the Octave (GUI) shortcut on the desktop, or find the Octave item and click it in the start menu Panels of the Octave desktop (in the default layout) File Browser Command Window Workspace Command History

27 Graphical User Interface (GUI) of Octave File Browser Workspace Command Window Command History

28 Graphical User Interface (GUI) of Octave Setting the current directory (or folder) The selection of the current directory is important when we want to read data from files or save data into files or run our own scripts or call our own functions. The path of the current directory is displayed on the right side of the toolbar. We can take a step upwards in the directory system by clicking the green upwards arrow (One directory up). We can directly select any path by clicking the rightmost blue open folder icon. This action invokes a common dialog window "Browse directories". If the current directory has been changed, the content of the selected directory will be displayed in the "File Browser" window.

29 References