Get parameters.
        Args:
            grad_only (bool, optional): Return parameters with `need_grad` option as `True`. 
            If you set this option as `False`, All parameters are returned. Default is `True`.
        Returns:
            dict: The dictionary of parameter name (`str`) to Variable (:obj:`~nnabla.Variable`).

def get_parameters(self, grad_only=True):
        """Get parameters.
        Args:
            grad_only (bool, optional): Return parameters with `need_grad` option as `True`. 
            If you set this option as `False`, All parameters are returned. Default is `True`.
        Returns:
            dict: The dictionary of parameter name (`str`) to Variable (:obj:`~nnabla.Variable`).
        """
        params = OrderedDict()

        for v in self.get_modules():
            if not isinstance(v, tuple):
                continue
            prefix, module = v
            for k, v in module.__dict__.items():
                if not isinstance(v, nn.Variable):
                    continue
                pname = k
                name = "{}/{}".format(prefix, pname)
                if grad_only and v.need_grad == False:
                    continue
                params[name] = v
        return params