Adding chi examples

pynam/noise/chi.py

@@ -0,0 +1,19 @@
+from typing import Callable
+
+import numpy as np
+import scipy.integrate
+
+import pynam.noise.im_ref
+
+
+def get_chi_zz_e(eps: Callable[[float], complex]) -> Callable[[float], float]:
+	im_ref_p = pynam.noise.im_ref.get_im_ref_p(eps)
+
+	def chi_zz_e(z: float) -> float:
+
+		def integrand(y: float) -> float:
+			return (y**2) * im_ref_p(y / z) * np.exp(-2 * y)
+
+		return scipy.integrate.quad(integrand, 0, np.inf, epsabs=1e-10, epsrel=1e-10)[0] / (z**3)
+
+	return chi_zz_e