# Understanding MATLAB’s Graphing Techniques for Line Plots

In this article, we will delve into the intricacies of plotting multiple lines using MATLAB. We will explain the various approaches you can take to achieve your desired visualizations and provide code …

Updated November 1, 2023

*Hey! If you love Computer Vision and OpenCV as much as I do let's connect on Twitter or LinkedIn. I talk about this stuff all the time and build cool projects.*In this article, we will delve into the intricacies of plotting multiple lines using MATLAB. We will explain the various approaches you can take to achieve your desired visualizations and provide code samples to demonstrate different methods. This article is aimed at both beginners as well as advanced users who wish to explore more effective ways of utilizing MATLAB for their data analysis needs.

Introduction

MATLAB, a high-level programming language developed by MathWorks, has become an invaluable tool for engineers, scientists, and analysts alike due to its extensive capabilities for data manipulation and visualization. Among the plethora of functionalities it offers, one essential feature is plotting line charts or graphs that effectively illustrate numerical values with respect to time, position, or other variables. This ability to generate visually appealing line plots can play a significant role in decision-making processes or data interpretation.

In this article, we will focus on understanding the concepts and methodologies involved in generating multiple lines using MATLAB. Specifically, we will cover the following topics:

- Single Line Plot
- Multiple Line Plots with Hold
- Multiple Line Plots Using Linespace, Logspace, and Array Indexing
- Animation in MATLAB for Line Plots
- Adding Labels to Line Plots for Improved Visualization
- Optimizing Plot Customizations

Single Line Plot

A basic line plot using MATLAB involves plotting a single line with a particular set of data points, typically X-values and Y-values. Let’s begin by creating a simple example to demonstrate the basic syntax:

Create sample data: x = linspace(0,15,21); y = sin(x) + 2;

Plot a single line using these values: plot(x,y,'–', ‘LineWidth’,3)

In this example, we generated two vectors, ‘x’ and ‘y’. The vector ‘x’ contains linearly spaced data points between 0 and 15 at a step of 2/21. The vector ‘y’ is calculated from ‘x’ using the sine function along with a constant value 2 for added variety in the plot.

The plot command generates a figure, which uses the variables x and y to construct the line. Here, the line style is denoted by “–” and the line thickness is set to 3 by the property ‘LineWidth’. This basic syntax allows you to produce simple plots with minimal effort.

Multiple Line Plots with Hold

Another useful method in MATLAB for plotting multiple lines is using the hold command. By holding a graph object while adding new data, it maintains the previous lines on the same axis. To use this technique, we follow these steps:

Create sample data: x1 = linspace(0,15,21); y1 = sin(x1) + 2; x2 = linspace(10,30,20); y2 = cos(x2) * exp(x2);

Plot the first line: plot(x1,y1,'–', ‘LineWidth’,3) Hold the graph object for further additions: hold on Plot the second line: plot(x2,y2,'-', ‘LineWidth’,4) Release the graph object after completing the plot: hold off

In this example, we generated two sets of data to create a more diverse plot. Firstly, we plotted a sine wave using ‘x1’ and ‘y1’. Next, we defined another set of values (‘x2’, ‘y2’) representing a cosine function modified with an exponential term. We used the hold command to maintain our first line on the graph while generating the second line. Finally, we released the hold function once our objective was achieved.

Multiple Line Plots Using Linespace, Logspace, and Array Indexing

MATLAB offers various functions like linspace, logspace, and array indexing to generate multiple lines with finer control over data points, spacing, and visual representation. Let’s explore each function in detail:

- linspace(a,b,n) - Creates a vector of linearly spaced numbers from a to b with n equal increments between the elements.
- logspace(loga,logb,n) - Generates a vector of logarithmically spaced numbers in base 2 that grow from 2^loga to 2^logb in increments of n
- Array Indexing - Allows you to access elements of a given array based on their indices, which can be used to create multiple lines with various data sets.

To illustrate the usage of these functions, we will create an example combining them for plotting several lines:

Create sample data:
x1 = linspace(0,5,8); y1 = cos(2*pi*x1); x2 = logspace(-2,3,6); y2 = 2^x2; x3 = -2:0.1:3; y3 = exp(x3).^2;

Plot the lines using array indexing: plot([x1,x2,x3],[y1,y2,y3])

In this example, we defined three sets of data points (‘x1’, ‘y1’), (‘x2’, ‘y2’) and (‘x3’, ‘y3’) using linspace, logspace, and array indexing respectively. We then plotted all these lines together in a single figure by passing an array containing both the x-values and y-values of each set.

Animation in MATLAB for Line Plots

MATLAB also offers functionality to create animations that can be particularly useful when visualizing time-dependent data sets or processes with multiple steps. To demonstrate this, let’s build an example:

Create sample data: x = 0 : 1/25 : 5; y1 = sin(x); y2 = cos(x); y3 = exp(x);

Plot the lines and create an animation by incrementing ‘x’: for i = 1:length(x) plot(x,[y1,y2,y3]); hold on; redraw; pause(0.5); end

In this example, we generated three vectors representing a sine wave, a cosine function, and an exponential function. We then created an animation by looping through ‘x’ using the for loop while incrementing it. At each iteration of ‘i’, we plot the updated line using all three functions, hold them on the same graph, redraw the axes, wait with a pause, and continue to the next iteration. This results in an animated visualization of the multiple lines as they change over time.

Adding Labels to Line Plots for Improved Visualization

To enhance readability and make the plot more informative, we can add labels to the axes and lines in a MATLAB graph. Here is a simple example demonstrating these additional customizations:

Create sample data: x = linspace(0,15,21); y = sin(x) + 2;

Plot the line with labels for the X-axis, Y-axis, and line itself: plot(x,y,‘LineWidth’,3) title(‘Sample Line Plot - Linear Spaced Data’); xlabel(‘X-Axis Label’); ylabel(‘Y-Axis Label’); axis([0 15 -2 6]) hold on; plot(x,sin(x),'-.',‘LineWidth’,4); hold off legend(‘Original Line’,‘Modified Sine Wave’)

In this example, we have plotted a sine wave as seen before and added an additional line representing the modified sine function. We also customized our graph by labeling the X-axis, Y-axis, and setting limits for the axis. Lastly, we included labels to identify the original and modified lines in the legend.

Optimizing Plot Customizations

By combining various techniques discussed in this article, you can further fine-tune your plots to effectively convey your data’s essence. For example:

- Adjust line width for better visual distinction between lines
- Use different colors or styles for each line type to enhance readability
- Employ legends to highlight unique aspects of your plot
- Leverage text annotations and labels for additional information on the graph
- Explore 3D plots when the data allows for a deeper understanding of relationships between variables

In conclusion, MATLAB offers several methods to create line plots that cater to your needs. By utilizing these techniques effectively and optimizing visualization aspects such as line plotting, animation, and annotation, you can make valuable insights from your data more accessible and appealing.