text: import matplotlib.pyplot as plt
  import numpy as np
  
  from ifg import IfgCalculator
  
  # temps = np.logspace(-2, 4, num=100)
  thetas = np.linspace(0.5, 10.0, 1000)
  vols = [0.1, 1, 100]
  t = IfgCalculator(volumes=vols, thetas=thetas, output_in_si=False)
  asymp = np.ones_like(thetas) * 5 / 3
  
  plt.plot(thetas, t.C_P[:, 0] / t.C_V[:, 0], "k-", label=r"$v = 0.1$")
  # NOTE: does not depend on volume
  # plt.plot(thetas, t.C_P[:, 0] / t.C_V[:, 1], "k--", label=r"$v = 1$")
  # plt.plot(thetas, t.C_P[:, 0] / t.C_V[:, 2], "k-.", label=r"$v = 10$")
  plt.plot(thetas, asymp, "r--", label=r"High-$T$ asymp.")
  
  plt.xscale("log")
  plt.xlabel(r"$T$, Ha")
  plt.ylabel(r"$C_P / C_V$")
  # plt.xlim(1e-2, 1e4)
  # plt.ylim(0, 2)
  plt.legend()
  plt.text(200, 1.7, r"$C_P/C_V = 5/3$")
  plt.savefig("cp_by_cv.pdf", bbox_inches="tight")
  plt.show()
  