Error while calling a function a class

Hi all, Please help. I have a file with the name Bandit.m. It has a class defined Bandit. Code is as follows:

********************

classdef Bandit
    properties
        m 
        mean_val
        N

      end
      methods
          function self = Bandit(m)
              self.m = m;
              self.mean_val = 0;
              self.N = 0;

          end
          function  reward = pull_arm()
              reward = randn() + self.m;

          end

      end
  end

********************

Now, I have another file called test.m in the same directory. I run the following line and get the error. Code is as follows:

a = Bandit(5);
a.pull_arm();

when I run the above code, I get "Too many input arguments.". Am I doing some mistakes in the above 2 lines of code? I have been working with Python, but using MATLAB for the first time.

I am new to MATLAB. Can somebody help?

Answer 1

[Steven Lord]

" a.pull_arm();" is equivalent to "pull_arm(a);". [There could be a difference if your method accepted two inputs, but for this particular case there isn't.] From the documentation:

"MATLAB differs from languages like C++ and Java® in that there is no special hidden class object passed to all methods. You must pass an object of the class explicitly to the method. The left most argument does not need to be the class object, and the argument list can have multiple objects. MATLAB dispatches to the method defined by the class of the dominant argument."

You can name that explicit input argument self if you want.

function  reward = pull_arm(self)
  reward = randn() + self.m;
end

I suspect you may want pull_arm to update a property of the object self. If that's the case you need to do one of two things. The first approach would be to call the function with the object instance as both input and output:

function  self = pull_arm(self)
  self.m = randn() + self.m; % Assuming m is the cumulative reward
end

and invoke this method as:

myBandit = pull_arm(myBandit);

The second approach involves making your class a handle class.