How to Fix “Error using / Matrix dimensions must agree” in MATLAB

MATLAB is a helpful programming tool that allows us to perform various matrix operations as well as to plot functions in two or more dimensions. Sometimes while performing matrix, arithmetic operations, or plotting functions in multiple dimensions, we experience the “Error using / Matrix dimensions must agree” error in MATLAB. This type of error occurs in MATLAB due to different matrices’ sizes or dimensions.

If you are the one experiencing the same type of error, read this guide to fix it in MATLAB.

How does “Error using / Matrix dimensions must agree” Occur in MATLAB?

There are two main reasons for “Error using / Matrix dimensions must agree” to occur in MATLAB, which are as follows:

Matrices do not have the same size while performing element-wise dot operations.
Plot two or more data sets of different lengths.

How to Fix “Error using / Matrix dimensions must agree” in MATLAB?

The error “Error using / Matrix dimensions must agree” can be fixed by:

Defining two or more matrices of the same size while performing element-wise division using dot operation.
While plotting two or more data sets, all of them must be of the same length.

Examples

Follow these examples to learn how to fix the “Error using / Matrix dimensions must agree” in MATLAB.

Example 1: How to Fix the Error “Error using / Matrix dimensions must agree” While Performing Matrices or Arithmetic Operations?

In this example, we define a vector x and a vector y, a function of x. Then we perform an element-wise multiplication operation between these two vectors.

x = -1.5:0.1:1.5;
y = 1/sqrt(x);
z = x.*y

When we execute this code, we get an “Error using / Matrix dimensions must agree” as shown on the screen.

This error occurred in line 2 because we did not perform element-wise operations while calculating y corresponding to each element of x. This error can be fixed using a dot operator that performs element-wise operation between x and y.

x = -1.5:0.1:1.5;
y = 1./sqrt(x);
z = x.*y

Example 2: How to Fix this Error “Error using / Matrix dimensions must agree” while Plotting a Function?

This example declares a vector x and defines a function y in terms of x. Then we plot x and y using MATLAB’s plot() function.

x = 1.5:0.1:3;
y = 1/sqrt(x);
plot(x, y)

This code generates an error “Error using / Matrix dimensions must agree” as shown on the screen.

The error occurred because y does not have the same length as x. After all, the dot operation is missing here. Using the dot operation, we can fix this error by defining y as having the same length as x.

x = 1.5:0.1:3;
y = 1./sqrt(x);
plot(x, y)

Conclusion

The “Error using / Matrix dimensions must agree” occurs in MATLAB while performing matrices or arithmetic operations or plotting functions with multiple dimensions. This error could be due to the incompatibility of the matrix sizes or dimensions involved in the operation. In this guide, we have explored the causes and fixes to overcome “Error using / Matrix dimensions must agree” in MATLAB. Understanding them will help you write efficient and error-free code in MATLAB.