**Course Title:** MATLAB Programming: Applications in Engineering, Data Science, and Simulation **Section Title:** Functions and Scripts in MATLAB **Topic:** Creating and Calling Custom Functions In the previous topic, we covered the basics of MATLAB scripts and functions, defining their characteristics, and their role in MATLAB programming. In this topic, we will explore the process of creating and calling custom functions in MATLAB, including their syntax, functionality, and use cases. ### Function Syntax In MATLAB, a function is defined using the `function` keyword followed by the function name, input arguments, and output arguments. The general syntax for a MATLAB function is: ```matlab function [output_args] = function_name(input_args) % function code end ``` Let's break down the syntax: * **`function` keyword:** This keyword indicates the start of the function definition. * **`output_args` (output arguments):** These are the variables that will be returned by the function. You can have multiple output arguments separated by commas. * **`function_name` (function name):** This is the name given to the function. It should be a unique and descriptive name that indicates the function's purpose. * **`input_args` (input arguments):** These are the variables that you pass to the function when calling it. You can have multiple input arguments separated by commas. * **`function code` (function body):** This is where you write the code that performs the desired operations using the input arguments and returns the output arguments. Here's a simple example of a custom function that calculates the area of a rectangle: ```matlab function [area] = calculate_area(length, width) area = length * width; end ``` This function takes two input arguments, `length` and `width`, and returns one output argument, `area`. For more information on MATLAB functions and their syntax, you can refer to the official MATLAB documentation: [Functions (MATLAB)](https://www.mathworks.com/help/matlab/functions.html). ### Calling Custom Functions Once you have defined a custom function, you can call it in your MATLAB code by using the function name followed by the input arguments in parentheses. Here's how to call the `calculate_area` function we created earlier: ```matlab rectangle_length = 5; rectangle_width = 3; area = calculate_area(rectangle_length, rectangle_width); disp(area); // Outputs: 15 ``` In this example, we first define the input arguments `rectangle_length` and `rectangle_width`. Then, we call the `calculate_area` function, passing these input arguments, and store the returned output argument `area` in a variable. Finally, we display the calculated area using the `disp` function. ### Function Files In MATLAB, custom functions are typically stored in separate files with a `.m` extension, known as function files. When creating a function file, the filename should match the function name. For instance, the `calculate_area` function we defined earlier would be stored in a file named `calculate_area.m`. Function files can be created using the MATLAB editor or any other text editor. To create a new function file in the MATLAB editor, follow these steps: 1. Open the MATLAB editor by navigating to **Home** > **New Script** or by pressing `Ctrl + N` (Windows) or `Cmd + N` (Mac). 2. In the new script, define your function using the syntax described earlier. 3. Save the file with a `.m` extension and a filename that matches the function name. ### Practical Takeaways and Example Creating custom functions is a fundamental aspect of MATLAB programming, allowing you to organize and reuse your code efficiently. Here are some practical takeaways to keep in mind: * **Use descriptive function names:** Choose function names that accurately describe the function's purpose and are easy to understand. * **Keep functions concise:** Break down complex tasks into smaller, manageable functions that perform specific operations. * **Test your functions:** Verify the correctness of your functions by calling them with sample input arguments and checking the returned output arguments. Here's a more comprehensive example that demonstrates the use of custom functions in a real-world application: Suppose you want to calculate the average of a list of numbers. You can create a custom function `calculate_average` that takes a list of numbers as input and returns the calculated average. ```matlab % calculate_average.m function [average] = calculate_average(numbers) total_sum = sum(numbers); average = total_sum / length(numbers); end % Call the calculate_average function numbers = [10, 20, 30, 40, 50]; average = calculate_average(numbers); disp(average); // Outputs: 30 ``` This example demonstrates the creation of a custom function `calculate_average` and its use in calculating the average of a list of numbers. ### Conclusion Creating and calling custom functions are essential skills in MATLAB programming, enabling you to organize and reuse your code efficiently. By following the syntax and guidelines outlined in this topic, you can start building your own custom functions to solve complex problems and applications. **Exercise:** * Create a custom function `calculate_circle_area` that calculates the area of a circle given its radius. * Test the function with sample input arguments and verify its correctness. If you have any questions or concerns about this topic or need help with the exercise, please feel free to ask.