Question

I used MatlabConrol to connect Java and MATLAB. I want to send an image path to MATLAB to process it with matching functions and give me back a number of similar images and paths, to show in the Java GUI.

I always get the same error when passing an image path to MATLAB:

Error using eval
Undefined function 'getinput' for input arguments of type 'char'.

Here’s my MATLAB function:

function matlab = getinput(input)
results = hgr(input);

And my Java code:

imag = ImageIO.read(fileChoose.getSelectedFile());
ImagePath = fileChoose.getSelectedFile().getAbsolutePath();

public void SendingMatlabControl() throws MatlabConnectionException,
  MatlabInvocationException {
  // create proxy
  MatlabProxy proxy;
  // Create a proxy, which we will use to control MATLAB
  MatlabProxyFactory factory = new MatlabProxyFactory();
  proxy = factory.getProxy();
  // Display 'hello world' like before, but this time using feval
    try {
      // call builtin function
      proxy.eval("getinput('imagepath')");
      // call user-defined function (must be on the path)
      proxy.eval("addpath('E:\\vm')");
      proxy.feval("matlab");
      proxy.eval("rmpath('E:\\vm)");
    } catch (MatlabInvocationException e) {
      // TODO Auto-generated catch block
      e.printStackTrace();
    }
    // Disconnect the proxy from MatLab
    proxy.disconnect();
  }

Answer 1

Let me give an example of calling a function, passing it input, and retrieving the output. There are two ways, either:

• use eval and assign the result of the function inside the MATLAB workspace, then retrieve those variables using getVariable, or
• use returningFeval to evaluate the function with its inputs, and directly retrieve the output.

Suppose we had a MATLAB function myfunc.m that takes a string as input, and returns a cell array containing a string, a number, and a vector:

function out = myfunc(str)
    out = cell(3,1);
    out{1} = sprintf('Welcome to %s!', str);
    out{2} = 99;
    out{3} = rand(10,1);
end

Here is the Java code:

import matlabcontrol.*;

public class TestMyFunc
{
    public static void main(String[] args)
        throws MatlabConnectionException, MatlabInvocationException
    {
        // create proxy
         MatlabProxyFactoryOptions options =
            new MatlabProxyFactoryOptions.Builder()
                .setUsePreviouslyControlledSession(true).build();
        MatlabProxyFactory factory = new MatlabProxyFactory(options);
        MatlabProxy proxy = factory.getProxy();

        // call function and get output cell array
        String in = "Stack Overflow";
        Object[] out = proxy.returningFeval("myfunc", 1, in);

        // extract stuff from cell array
        out = (Object[]) out[0];
        String str = (String) out[0];
        double x = ((double[]) out[1])[0];
        double[] arr = (double[]) out[2];

        // show result
        System.out.println("str =\n " + str);
        System.out.println("x = \n " + x);
        System.out.println("arr =");
        for(int i=0; i < arr.length; i++) {
            System.out.println(" " + arr[i]);
        }

        // shutdown MATLAB
        //proxy.feval("quit");

        // close connection
        proxy.disconnect();
    }
}

I get the output:

str =
 Welcome to Stack Overflow!
x =
 99.0
arr =
 0.5974901918725793
 0.3353113307052461
 0.29922502333310663
 0.45259254156932405
 0.42264565322046244
 0.35960631797223563
 0.5583191998692971
 0.7425453657019391
 0.42433478362569066
 0.42935578857620504