Minimal example for pdf mismatch in fluids

fluids_pdf_mismatch.py

import matplotlib.pyplot as plt
import numpy as np
import fluids.particle_size_distribution as psd

# Sizes
step = 2e-9
ds = np.arange(1e-9,500e-9,step)

# Artificial PSD with mean size at 50 nm and PDI 0.05
mu1 = 50e-9
sigma1 = 0.05*mu1
fractions = np.exp(-1.*(ds-mu1)**2/(2*sigma1)**2)

# Artificial PSD with mean size at 100 nm and PDI 0.05
mu2 = 100e-9
sigma2 = 0.05*mu2
fractions = fractions + np.exp(-1.*(ds-mu2)**2/(2*sigma2)**2)

# Normalization
fractions = fractions/fractions.sum()

# Plot the input pdf
plt.figure()
plt.plot(ds, fractions, label='input Volume pdf')

# Define the corresponding distribution in fluids - Volume/Mass weighted
fluids_psd = psd.ParticleSizeDistribution(ds=ds,
                                          fractions=fractions,
                                          order=3)
# Overlay the surface and mass-weighted distributions on top of the input
fluids_psd.plot_pdf((2,3), pts=fluids_psd.N)
# 2 issues:
# - the areas under the mass weighted data (input vs fluids) are different
# - the proportions of the populations do not match