# Resolving the 'Undefined Operator *' Error for Function_Handle Input Arguments: A Comprehensive Guide

If you're a developer working with MATLAB, chances are you've encountered the "Undefined operator '*' for input arguments of type 'function_handle'" error. This guide will provide a step-by-step solution to help you understand and resolve this issue. We'll also answer some frequently asked questions to give you a deeper understanding of the problem.

## Understanding the Error

The "Undefined operator '*' for input arguments of type 'function_handle'" error occurs when you try to perform a multiplication operation between function handles. In MATLAB, function handles are a way to represent and work with functions as variables. However, the multiplication operator `*` is not defined for function handles, leading to this error.

For example, consider the following code snippet:

``````f1 = @(x) x^2;
f2 = @(x) x^3;
result = f1 * f2;
``````

This code will generate the mentioned error, as we are trying to multiply two function handles `f1` and `f2` directly.

## Step-by-Step Solution

To resolve this error, you can follow the steps below:

Identify the problematic multiplication operation: In your code, find the line where the error is being generated. This will usually be a line where you're trying to multiply two function handles.

Wrap the functions in another function: Instead of multiplying the function handles directly, define a new function that takes the same input arguments and returns the product of the original functions' outputs.

For example, modify the previous code snippet as follows:

``````f1 = @(x) x^2;
f2 = @(x) x^3;
result = @(x) f1(x) * f2(x);
``````

Now, `result` is a new function handle that returns the product of `f1(x)` and `f2(x)` for any given `x`.

1. Test your updated code: Run your code again to ensure that the error is resolved and your updated function works as expected.

## FAQs

### 1. Can I use other arithmetic operations with function handles?

Yes, you can use addition, subtraction, and division operators with function handles. However, you should still follow the same approach described in the step-by-step solution to avoid potential errors.

### 2. How do I differentiate a function handle in MATLAB?

To differentiate a function handle, use the `diff` function from the Symbolic Math Toolbox. For example, you can differentiate the function handle `f = @(x) x^2` as follows:

``````syms x;
f = x^2;
df = diff(f, x);
``````

Now, `df` will contain the symbolic expression `2*x`.

### 3. Can I use the `*` operator with other data types in MATLAB?

Yes, the `*` operator is defined for several data types, such as numeric arrays, matrices, and strings. However, it is not defined for function handles, as explained in this guide.

### 4. How do I perform element-wise multiplication with function handles?

To perform element-wise multiplication with function handles, you can use the same approach described in the step-by-step solution, but replace the `*` operator with `.*` for element-wise multiplication.

### 5. Can I pass a function handle to another function in MATLAB?

Yes, you can pass a function handle as an input argument to another function. This is useful when you want to work with a function that takes another function as an argument, such as optimization or integration functions.

Remember, the key to resolving the "Undefined operator '*' for input arguments of type 'function_handle'" error is to avoid directly multiplying function handles. Instead, create a new function handle that returns the product of the original functions' outputs. And don't forget to check the MATLAB documentation for more answers and examples.

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