Troubleshooting Error: Function Value and Ydata Sizes Not Equal

Source: Mathworks


The "function value and Ydata sizes are not equal" error message is a common problem in MATLAB. This error occurs when plotting with a function using the plot function, and it can be caused by a variety of mistakes in data formatting or coding. This article provides an overview of the issue, step-by-step instructions for troubleshooting the issue, and an FAQ section to answer additional questions.


These troubleshooting steps will help you identify and resolve the issue.

Check your variables for proper size:

  • Make sure that the function or vector you are trying to plot is the same size as the YData vector. For example, if your function is a 2 x 1 vector, your YData vector should also be a 2 x 1 vector.

Check for missing data:

  • Make sure you are passing the right set of data points to the plot function. If you are missing data points, it could cause an error.

Check whether the variables are numbers or strings:

  • If the function is an array of numbers, make sure the YData vector has the same structure and contains numbers as well.

Check the function that is being called:

  • Make sure the function argument is valid. The plot function only accepts functions that output a single value per given value of the variable.

Check for syntax errors:

  • Make sure your code does not contain any syntax errors which could prevent the plot function from working correctly.


Q: What causes the 'Function value and Ydata sizes are not equal' error?
A: This error is caused by mistakes in data formatting or coding. Common causes include passing the wrong set of data points to the plot function, passing variables of different sizes to the plot function, and writing invalid function arguments.

Q: How do I fix the 'Function value and Ydata sizes are not equal' error?
A: To fix the error, follow the troubleshooting steps listed above, such as checking the function and variables for proper size, making sure all data points are included, and checking for syntax errors.

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