1.4. Getting started

MATLAB variables are created with an assignment statement. The syntax of variable assignment is

variable name = a value (or an expression)

For example,

>> x = expression

where expression is a combination of numerical values, mathematical operators, variables, and function calls. In other words, expression can involve:

• manual entry
• built-in functions
• user-defined functions.

In MATLAB, creating a variable is simple. You use the equals sign (=) to assign a value or an expression to a variable name. For instance, if you want to store the result of a calculation like 5 + 3, you would write: x = 5 + 3. Here, x is the variable name, and it will hold the value 8. This assignment can also include more complex operations, which can involve functions and other variables.

Think of variables like labeled boxes where you store items. If you have a box labeled 'x', you can put a specific toy (like the number 8) inside it. Then, every time you want the toy, you just ask for box 'x' instead of looking through everything to find it.

Once a variable has been created, it can be reassigned. In addition, if you do not wish to see the intermediate results, you can suppress the numerical output by putting a semicolon (;) at the end of the line. Then the sequence of commands looks like this:

>> t = 5;
>> t = t + 1

The output would be:

t = 6

In MATLAB, you can easily change the value stored in a variable. For example, if you initially set t to 5, you can later update t by adding 1 to its current value. Using a semicolon at the end of a command tells MATLAB not to show the result immediately, which can keep your workspace tidy.

Imagine you have a jar filled with 5 candies. If you decide to add one more candy, you can replace the amount in the jar with the new total (now 6). The semicolon is like a lid on the jar that prevents others from seeing how many candies you initially had until you're ready to share.

If we enter an expression incorrectly, MATLAB will return an error message. For example, in the following, we left out the multiplication sign, *, in the following expression:

>> x = 10;
>> 5x
??? 5x
|
Error: Unexpected MATLAB expression.

MATLAB provides feedback when something is wrong with your code. If you forget to include necessary operators, like the multiplication sign (*), MATLAB will display an error message, indicating that it couldn't understand what you intended to do. This immediate feedback is crucial for debugging and fixing errors.

Think of it like a math test where you accidentally miss adding a plus or multiplication sign. Your teacher (MATLAB) would circle that mistake and say, 'This doesn't make sense!' This helps you realize you need to correct that part of your work.

To make corrections, we can, of course, retype the expressions. But if the expression is lengthy, we make more mistakes by typing a second time. A previously typed command can be recalled with the up-arrow key. When the command is displayed at the command prompt, it can be modified if needed and executed.

In MATLAB, if you've entered a command but need to correct it, you don’t have to type it out all over again. Instead, you can simply press the up-arrow key to bring back the last command you typed. This saves time and reduces the chances of introducing more errors when retyping long expressions.

Imagine writing notes in your notebook. If you want to change something you just wrote, instead of rewriting the whole page, you can just erase a word or phrase. Similarly, using the up-arrow in MATLAB allows you to easily modify your last command without starting from scratch.

The order in which MATLAB performs arithmetic operations is exactly that taught in high school algebra courses. Exponentiations are done first, followed by multiplications and divisions, and finally by additions and subtractions. However, the standard order of precedence can be changed by inserting parentheses. For example,

>> (1 + 2) * 3
ans =
9

and from a previous example

>> 1 + 2 * 3
ans =
7

MATLAB follows the established order of operations, often remembered by the acronym PEMDAS (Parentheses, Exponents, Multiplication and Division, Addition and Subtraction). This means that when you write expressions, you must be mindful of how MATLAB will interpret them based on this order. However, you can control this sequence by using parentheses to clarify your intent.

Consider baking a cake where you have a recipe that says to mix the dry ingredients first (let's say flour, sugar, and baking powder) and then add the wet ingredients (like eggs and milk). If you don’t follow that order and just throw everything into the bowl without organization, the result might not turn out well. Similarly, using parentheses helps you ensure that MATLAB processes the calculations in the order you specify.

MATLAB by default displays only 4 decimals in the result of the calculations, for example, 163.6667. The command format controls how the results of computations are displayed. Here are some examples of the different formats together with the resulting outputs:

>> format short
>> x = -163.6667

>> format long
>> x = -1.636666666666667e+002

MATLAB's output display of numbers can be adjusted using the format command. By default, MATLAB shows 4 decimal places, which might not always be sufficient for your needs. If you require more precision, you can switch to 'long' format to see up to 15 digits. This feature is particularly useful in precise calculations like scientific computing.

Think of measuring your height. If someone tells you they are 'approximately' 5 feet 10 inches, that's fine for most contexts. But if you're an architect designing a building, you need to know the exact measurements down to the last millimeter. In MATLAB, changing formats lets you adjust the level of detail in your calculations based on your requirements.

The contents of the workspace persist between the executions of separate commands. Therefore, it is possible for the results of one problem to have an effect on the next one. To avoid this possibility, it is a good idea to issue a clear command at the start of each new independent calculation.

>> clear

The workspace in MATLAB holds all the variables and their values that you've defined during your session. However, these variables can carry over between commands. Using the clear command at the beginning of a new calculation helps ensure that previous variables don't unintentionally influence your work, leading to more accurate results.

Imagine your desk is cluttered with old papers from previous projects. If you start a new project without clearing away the old papers, you might confuse your current tasks with past ones. Similarly, using clear in MATLAB is like tidying up your workspace to ensure you can focus solely on the new calculations at hand.

To view the online documentation, select MATLAB Help from Help menu or MATLAB Help directly in the Command Window. The preferred method is to use the Help Browser. The Help Browser can be started by selecting the ? icon from the desktop toolbar. Information about any command is available by typing

>> help Command

MATLAB is a complex software tool, so it offers various ways to access help and documentation. By clicking on the Help menu or using the 'help' command, you can pull up detailed information about specific functions or topics that may confuse you. This can significantly enhance your learning process and troubleshooting.

Imagine trying to fix a complicated device without a user manual. Frustrating, right? But having a manual handy means you can look up instructions anytime you encounter a problem. Similarly, MATLAB's help features serve as your manual, providing support as you learn how to navigate the software.

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