def access_to_sympy(self, var_name, access):
        """
        Transform a (multidimensional) variable access to a flattend sympy expression.

        Also works with flat array accesses.
        """
        base_sizes = self.variables[var_name][1]

        expr = sympy.Number(0)

        for dimension, a in enumerate(access):
            base_size = reduce(operator.mul, base_sizes[dimension+1:], sympy.Integer(1))

            expr += base_size*a

        return expr