def METHOD_NAME(self):
    """
    Updates the size variables of all unknowns.
    """
    for u in self.unknowns:
        if u.name == 'f_hot':
            u.setSizes(nr=self.nr, nxi=self.hot_nxi, np=self.hot_np)
        elif u.name == 'f_re':
            u.setSizes(nr=self.nr, nxi=self.re_nxi, np=self.re_np)
        elif u.name == 'n_i':
            u.setSizes(nZ0=self.nZ0, nr=self.nr)
        elif u.size == self.nr:     # Fluid quantity
            u.setSizes(nr=self.nr)
        elif u.size == self.nions*self.nr:      # N_i or W_i
            u.setSizes(nions=self.nions, nr=self.nr)