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To call a user-defined MATLAB function from Java using matlabcontrol.jar, you need to follow these steps:

1. Add the matlabcontrol.jar file to your Java classpath.
2. Create a MatlabProxyFactory object to establish a connection to the MATLAB engine. This object will create instances of MatlabProxy which will be used to communicate with the MATLAB engine.
3. Use the MatlabProxyFactory object to create a MatlabProxy instance.
4. Use the MatlabProxy instance to execute the MATLAB function by calling the feval() method with the name of the function and any input arguments.
5. Capture the output of the MATLAB function using the MatlabProxy instance.

Here is an example code snippet that demonstrates how to call a user-defined MATLAB function from Java using matlabcontrol.jar: 

import matlabcontrol.*;

public class MatlabCaller {
   public static void main(String[] args) throws MatlabConnectionException, MatlabInvocationException {
      // Create a proxy factory to connect to the MATLAB engine
      MatlabProxyFactory factory = new MatlabProxyFactory();
      
      // Create a proxy, which will communicate with the MATLAB engine
      MatlabProxy proxy = factory.getProxy();
      
      // Call the MATLAB function with input arguments
      Object[] result = proxy.feval("my_matlab_function", arg1, arg2, arg3);
      
      // Display the output of the MATLAB function
      System.out.println(result[0]);
      
      // Disconnect the proxy from the MATLAB engine
      proxy.disconnect();
   }
}

In this example, replace my_matlab_function with the name of your user-defined MATLAB function, and arg1, arg2, and arg3 with any input arguments required by the function. The output of the function will be returned as an array of Object objects, which you can access using the indexing operator ([]).