Add example to show how to create a custom Exposition class

[RemDelaporteMathurin]

Users might be interested in creating custom classes to process files.

For instance, add a non-instantaneous recombination coefficient to compute the surface concentration more accurately.

This is an example.

What do you think @ehodille?

import numpy as np

import divHretention


class ExpositionWithRecombination(divHretention.Exposition):
    def __init__(self, filename, filetype):
        super().__init__(filename, filetype)

    def compute_surface_concentration(self):
        super().compute_surface_concentration()

        k_B = 8.6e-5
        K_0_W = 1e-12
        E_K_W = 0.8
        K = K_0_W*np.exp(-E_K_W/k_B/self.temperature)
        self.concentration += (self.ion_flux/K)**0.5
        self.concentration += (self.atom_flux/K)**0.5


filename = "data/exposure_conditions_divertor/WEST/West-LSN-P1.6e+21-IP0.449MW.csv"

my_recomb_exp = ExpositionWithRecombination(filename, "WEST")
my_exp = divHretention.Exposition(filename, "WEST")


import matplotlib.pyplot as plt

plt.plot(my_recomb_exp.arc_length, my_recomb_exp.inventory)
plt.plot(my_exp.arc_length, my_exp.inventory)
plt.annotate(
    "Non-instantaneous \n recombination",
    (my_recomb_exp.arc_length[-1], my_recomb_exp.inventory[-1]))
plt.annotate(
    "Instantaneous",
    (my_exp.arc_length[-1], my_exp.inventory[-1]))
plt.yscale("log")
plt.xlim(right=0.8)
plt.xlabel("Arc length (m)")
plt.ylabel("Inventory (H/m)")
plt.show()