One-layer Vs profiles crash HH parameter and damping calibration with IndexError #119

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

Problem

A one-layer Vs profile is accepted by Vs_Profile() and by check_Vs_profile_format(), then crashes HH parameter and damping calibration with IndexError.

hh_param_from_profile(), hh_param_from_curves(), and Damping_Calibration.get_damping_curves() always drop the last row as the halfspace (vs_profile[:-1, ...]) and then index that slice with [-1]. With one layer the slice is empty.

• One soil layer and no halfspace (n_layer == 1) is discarded, so there is nothing left to calibrate.
• A single halfspace (n_layer == 0) has no soil layer. That should be a ValueError, not an IndexError.

A two-row profile (one soil layer plus a halfspace) works.

import numpy as np
from PySeismoSoil.class_Vs_profile import Vs_Profile
from PySeismoSoil.class_damping_calibration import Damping_Calibration
import PySeismoSoil.helper_hh_calibration as hhc

one_layer = np.array([[10.0, 200.0]])
prof = Vs_Profile(one_layer)
print(prof.n_layer)  # 1

Damping_Calibration(prof).get_damping_curves()
# IndexError in _calc_vertical_stress: h[-1] on an empty array
# (also a RuntimeWarning: Mean of empty slice)

hhc.hh_param_from_profile(one_layer, verbose=False)
# IndexError in thk2dep: thk[-1] on an empty array

hhc.hh_param_from_curves(one_layer, np.zeros((2, 4)), verbose=False)
# same IndexError in thk2dep

Fix

After the halfspace is removed, if no soil layer remains, raise ValueError naming that case. If the profile is a single soil layer (last thickness > 0), keep that layer instead of dropping it. thk2dep() and _calc_vertical_stress() should also reject an empty thickness array with ValueError rather than indexing [-1].