fit_HH_x_single_layer() and fit_H4_x_single_layer() subtract the initial damping in place, changing the Damping_Curve's data and the caller's array #84

Found while reviewing #74. Pre-existing on main (b764057); #74 does not change the behavior.

Problem

fit_HH_x_single_layer() and fit_H4_x_single_layer() offset the damping curve with damping_data_in_pct[:, 1] -= init_damping. This writes into the array that the caller passed in.

Damping_Curve.get_HH_x_param() and get_H4_x_param() pass self.raw_data. Multiple_Damping_Curves.get_all_HH_x_params() and get_all_H4_x_params() pass each curve's raw_data through fit_all_damping_curves(), which uses the arrays as is.

When the curve is not interpolated, Curve.__init__() stores raw_data as the caller's array, and damping is a view of its second column. So after a fit, the curve's damping, its raw_data, the caller's array, and get_curve_matrix() are all shifted down by the initial damping.

import numpy as np

from PySeismoSoil.class_curves import Damping_Curve, Multiple_Damping_Curves

data = np.genfromtxt('tests/files/curve_FKSH14.txt')[:, 2:4]  # strain [%], damping [%]

user_array = data.copy()
curve = Damping_Curve(user_array)
print(curve.damping[:3], user_array[:3, 1])
# [1.6683 1.8386 2.4095] [1.6683 1.8386 2.4095]
curve.get_HH_x_param(pop_size=1, n_gen=1)
print(curve.damping[:3], curve.raw_data[:3, 1], user_array[:3, 1])
# [0.     0.1703 0.7412] [0.     0.1703 0.7412] [0.     0.1703 0.7412]
# (expected [1.6683 1.8386 2.4095] for all three)

curve_2 = Damping_Curve(data.copy())
curve_2.get_H4_x_param(pop_size=1, n_gen=1)
print(curve_2.damping[:3])
# [0.     0.1703 0.7412]

mdc = Multiple_Damping_Curves('tests/files/curve_FKSH14.txt')[:2]
mdc.get_all_HH_x_params(pop_size=1, n_gen=1)
print(mdc[0].damping[:3], mdc.get_curve_matrix()[:3, 3])
# [0.     0.1703 0.7412] [0.     0.1703 0.7412]

mdc_2 = Multiple_Damping_Curves('tests/files/curve_FKSH14.txt')[:2]
mdc_2.get_all_H4_x_params(pop_size=1, n_gen=1)
print(mdc_2[0].damping[:3])
# [0.     0.1703 0.7412]

Fix

1. In fit_HH_x_single_layer() and fit_H4_x_single_layer(), work on a float copy: for example damping_data_in_pct = np.array(damping_data_in_pct, dtype=float) before the offset. This keeps the caller's array, and so the curve objects, unchanged.
2. Add tests that Damping_Curve.get_HH_x_param() / get_H4_x_param() and Multiple_Damping_Curves.get_all_HH_x_params() / get_all_H4_x_params() leave curve.damping, curve.raw_data and the input array unchanged.