code: def matrix(self, title=None):
          
          if title is None:
              return javabridge.call(self.jobject, "toMatrixString", "()Ljava/lang/String;")
          else:
              return javabridge.call(self.jobject, "toMatrixString", "(Ljava/lang/String;)Ljava/lang/String;", title)
docs: Generates the confusion matrix.
  
          :param title: optional title
          :type title: str
          :return: the matrix
          :rtype: str