def forward(self, variables: List[Variable]) -> Variable:
        """
        Performs the forward pass of the sum (concatenation) operation.

        :param variables: The list of variables to be summed.
        :type variables: List[Variable]
        :return: A new variable representing the sum of the input variables.
        :rtype: Variable
        """
        concat_values = "\n".join([v.get_value() for v in variables])
        role_descriptions = set([v.get_role_description() for v in variables])
        role_descriptions = ", ".join(role_descriptions)
        
        total = Variable(
            value=concat_values,
            predecessors=variables,
            role_description=f"a combination of the following: {role_descriptions}",
            requires_grad=any([v.requires_grad for v in variables]),
        )
        
        total.set_grad_fn(BackwardContext(backward_fn=self.backward,
                                          summation=total))
        
        return total

        Performs the forward pass of the sum (concatenation) operation.

        :param variables: The list of variables to be summed.
        :type variables: List[Variable]
        :return: A new variable representing the sum of the input variables.
        :rtype: Variable
        
textgrad/autograd/algebra.py