Commit2 JT 111919

- renaming validation directory

examples/SPIN/test_problems/validation_langevin_precession/langevin.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+
+#Program fitting the exchange interaction
+#Model curve: Bethe-Slater function
+import numpy as np, pylab, tkinter
+import matplotlib.pyplot as plt
+import mpmath as mp
+# from scipy.optimize import curve_fit
+# from decimal import *
+
+mub=5.78901e-5          # Bohr magneton (eV/T)
+kb=8.617333262145e-5    # Boltzman constant (eV/K)
+g=2.0                   # Lande factor (adim)
+
+Hz=10.0                # mag. field (T)
+
+#Definition of the Langevin function
+def func(t):
+    return mp.coth(g*mub*Hz/(kb*t))-1.0/(g*mub*Hz/(kb*t))
+
+npoints=200
+ti=0.01
+tf=20.0
+for i in range (0,npoints): 
+    temp=ti+i*(tf-ti)/npoints
+    print('%lf %lf %lf' % (temp,func(temp),-g*mub*Hz*func(temp)))
+