4. Introduction to programming in MATLAB

So far in these lab sessions, all the commands were executed in the Command Window. The problem is that the commands entered in the Command Window cannot be saved and executed again for several times. Therefore, a different way of executing repeatedly commands with MATLAB is: 1. to create a file with a list of commands, 2. save the file, and 3. run the file. If needed, corrections or changes can be made to the commands in the file. The files that are used for this purpose are called script files or scripts for short.

In MATLAB, when you execute commands in the Command Window, those commands disappear once the session ends. To overcome this limitation, you can create script files, which are saved text files that contain a series of MATLAB commands. You can save these files, modify them as needed, and run them multiple times without needing to retype your commands.

Think of script files as recipes for cooking. Instead of remembering the steps every time you want to cook a dish, you write the recipe on paper. You can refer to it, make modifications as you like, and share it with others. Similarly, script files allow you to save your MATLAB commands, refer back to them, and even give them to fellow students.

A script file is an external file that contains a sequence of MATLAB statements. Script files have a filename extension .m and are often called M-files. M-files can be scripts that simply execute a series of MATLAB statements, or they can be functions that can accept arguments and can produce one or more outputs.

M-File scripts are files saved with a .m extension containing MATLAB code. These scripts can either be simple sequences of commands that MATLAB executes one by one or more complex scripts called functions. Functions are special types of M-Files that can take inputs, process them, and return outputs, allowing for much more flexible programming.

Imagine writing a play. You create a script that details the dialogues and actions of characters (like an M-File script). If you want to add a new character or change a scene, you can easily edit the script. On the other hand, if the script also specifies conditions for how characters should act (like functions), you can create unique interactions based on different scenarios.

Here are two simple scripts. Example 1... Save the file, for example, example1.m. Run the file, in the command line, by typing: >> example1 x = -0.5000 1.5000 -0.5000.

In Example 1, we create a script to solve a system of equations using MATLAB. We declare a matrix A and a vector b, which represent the equations' coefficients and constants, respectively. By running the script, MATLAB calculates the values of x that satisfy the equations, demonstrating how scripts can automate complex calculations efficiently.

Think about it like using a calculator for a math problem. Instead of doing each calculation step-by-step in your head, you write everything down in an organized way that the calculator understands and then press 'equals' to get your answer. The script automates the calculations for you, just as the calculator does.

All variables created in a script file are added to the workspace. This may have undesirable effects, because: Variables already existing in the workspace may be overwritten. The execution of the script can be affected by the state variables in the workspace. As a result, because scripts have some undesirable side-effects, it is better to code any complicated applications using rather function M-file.

When you create variables within a script file, those variables are added to the MATLAB workspace. This can lead to issues if the variable names conflict with existing variables, potentially causing errors or overwriting values unintentionally. For this reason, using functions is often recommended, as they have their own internal workspace.

Imagine mixing paints where each color represents a variable. If you pour a new color into your mixing pot without thinking, it might change the colors you initially had, leading to unexpected results. Functions in MATLAB are like separate jars of paint. When you’re done mixing in a jar, you can keep it safe and not worry about it affecting the other colors in your studio.

As mentioned earlier, functions are programs (or routines) that accept input arguments and return output arguments. Each M-file function (or function or M-file for short) has its own area of workspace, separated from the MATLAB base workspace.

Functions in MATLAB are specialized scripts that can take inputs and provide outputs. Unlike regular scripts, which share variables with the workspace, functions have their own internal workspace. This means changes in functions do not affect other variables outside of them. This feature helps avoid errors and makes code more modular.

Think of a function as a vending machine. You put in a coin (input), select a snack (processing), and the machine gives you a snack (output). The machine operates independently of other machines (other functions), meaning you can use multiple machines without them interfering with one another.

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