import numpy as np
import matplotlib.pyplot as plt
from crystals import Crystal
from skued import patterson
from skued import powdersim # To simulate experimental data

# Simulation of polycrystalline diffraction pattern
# for monoclinic VO2
cryst = Crystal.from_database('vo2-m1')
q = np.linspace(0.2, 10, 1024)
I = powdersim(cryst, q)

# Determination of the pair-pair distribution function
rr = np.linspace(1, 5, 256)
pairdist = patterson(q = q, I = I, crystal = cryst, radii = rr)

fig, ax = plt.subplots(1,1)
ax.plot(rr, pairdist, '.k')
ax.set_xlabel('Radial distance $\AA$')
ax.set_ylabel('Pair-pair correlation [a.u.]')