# Combining Two Matrices in MATLAB

In this article, we will delve into the topic of combining two matrices in MATLAB. As a Python Engineer and Computer Vision Expert who is well-versed in MATLAB and its capabilities, we understand the …

Updated November 21, 2023

In this article, we will delve into the topic of combining two matrices in MATLAB. As a Python Engineer and Computer Vision Expert who is well-versed in MATLAB and its capabilities, we understand the importance of matrix manipulations to solve complex problems across various domains such as data analysis, signal processing, machine learning, computer vision, and more. We will not only explain how these concepts apply in MATLAB but also demonstrate their use through code samples that will help you gain a deeper understanding. So, without further ado, let’s dive right into the world of combining matrices in this powerful programming language.

Before we begin with the main topic, it is crucial to have a solid grasp on what matrices are and their importance. Matrices are rectangular arrays of numbers or other data types that can be arranged in rows and columns. They play a significant role across various fields, including scientific computing, engineering, finance, and more. MATLAB has numerous functions that enable you to perform different matrix operations, such as addition, multiplication, subtraction, and more.

Let’s start with the basic concept of how to combine two matrices using the most fundamental operation – matrix addition. This is analogous to adding two numbers or vectors in a similar manner as follows:

1 + 2 = 3 (adding two scalars) [3 4] + [5 6] = [8 10] (addition of two matrices with the same dimensions)

Now, let’s move on to combining two matrices in MATLAB by utilizing its built-in functions. For this purpose, we will focus mainly on two primary functions: `+` and `vertcat`.

1. Adding Two Matrices Using the Plus Operator ‘+’

To perform matrix addition using the ‘+’ operator, you need to have two matrices with matching sizes in rows and columns. If the dimensions of both matrices are identical, MATLAB will automatically perform element-wise addition. Here is an example:

A = [3 4; 6 5]; B = [1 2; 7 8]; C = A + B;

C = 4 6 13 13

In the above code, we have defined two matrices (A and B) and combined them using the ‘+’ operator to create a new matrix (C). The resulting matrix C has been formed by adding the corresponding elements of A and B together. For example, in row 1 column 1, we get the result 4 + 1 = 5; similarly, 6 + 7 = 13 for the first element in row 2.

1. Adding Two Matrices Using the ‘vertcat’ Function

MATLAB also offers the `vertcat` function to combine two or more matrices along a specified dimension (either rows or columns). This method is particularly useful when you want to join matrices that may have different dimensions. However, ensure that the matrices being combined have at least one compatible dimension.

For example:

A = [1 2; 3 4]; B = [5 6; 7 8]; C = vertcat(A, B);

C = 1 2 5 6 3 4 7 8

Here, we have utilized the `vertcat` function to combine two matrices (A and B) that do not have identical dimensions. The function concatenates these matrices along the rows such that they become one matrix with the same size as A but having a greater number of columns. Note that the order of the input arguments in the `vertcat` function is important for ensuring compatibility, starting from the first matrix (A) followed by the second matrix (B), and so on.

1. Combining Two Matrices Using a Custom Function ‘matrixAddition’

While MATLAB provides two built-in methods to combine matrices as described above, you can also create your custom function for this purpose. This might be beneficial when you have specific requirements or prefer more control over the matrix combination process. The `matrixAddition` function below takes two input matrices (A and B) and returns a new matrix (C) by combining them along their specified dimensions:

function C = matrixAddition(A, B, dim1, dim2) % Adding two matrices along the specified dimension if ~isempty(dim1) && isempty(dim2) m = size(A,dim1); n = size(B,dim1); C = zeros(m,n); for i=1:m for j=1:n C(i,j) = A(i,j) + B(i,j); end end else if isempty(dim1) && ~isempty(dim2) m = size(A,dim2); n = size(B,dim2); C = zeros(m,n); for i=1:m for j=1:n C(i,j) = A(i,j) + B(i,j); end end else if isempty(dim1) && isempty(dim2) C = A + B; else error(‘Dimensions for adding matrices not specified properly.') end end

In the `matrixAddition` function, the first two conditions handle combining the matrices along rows and columns respectively, while the third condition caters to the default behavior when both dimensions are empty (i.e., matching dimensions for matrix addition).

To use this custom function, simply call it as follows:

A = [1 2; 3 4]; B = [5 6; 7 8]; C = matrixAddition(A, B);

In conclusion, understanding how to combine two matrices in MATLAB opens up a world of possibilities for data analysis, signal processing, machine learning, and computer vision applications. The three approaches presented above – using the ‘+’ operator, `vertcat` function, and the `matrixAddition` custom function – allow you to leverage matrix addition according to your specific requirements. As a Python Engineer and Computer Vision Expert, mastering these techniques and applying them appropriately will significantly enhance your skill set in various domains.