def METHOD_NAME(self, solver, x):
    self.xold = self.x
    self.x = x
    self.recold = self.rec
    self.rec = solver.Op @ x - solver.y
    if self.xold is not None:
        self.x_perc.append(
            100 * np.linalg.norm(self.x - self.xold) / np.linalg.norm(self.xold)
        )
        self.res_perc.append(
            100
            * np.linalg.norm(self.rec - self.recold)
            / np.linalg.norm(self.recold)
        )