docs: def pressision_try(orbitals, U, beta, step):
      """perform a better initial guess of lambda
         no improvement"""
      mu, lam = main(orbitals, U, beta, step)
      mu2, lam2 = linspace(0, U*orbitals, step), zeros(step)
      for i in range(99):
          lam2[i+1] = fsolve(restriction, lam2[i], (mu2[i+1], orbitals, U, beta))
      plot(mu2, 2*orbitals*fermi_dist(-(mu2+lam2), beta), label='Test guess')
      legend(loc=0)