linear_tf() frequency grid stops one step short of fmax for common inputs, including the defaults (fmax=30, freq_resolution=0.05) #98

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

Problem

linear_tf() sets the number of frequencies with int(np.floor_divide(fmax, freq_resolution)). np.floor_divide() rounds down the exact quotient of the two binary floats. 0.05 and 0.1 are stored as slightly more than 1/20 and 1/10, so np.floor_divide(30.0, 0.05) is 599.0, not 600.0. The grid then ends at 29.95 Hz, not at fmax. The docstring calls fmax the "Maximum frequency of interest".

Vs_Profile.get_ampl_function() and Vs_Profile.get_transfer_function() use this grid, with the same defaults. Vs_Profile.get_f0_RO() and get_f0_BH() call get_ampl_function() with the defaults, so they never look at 30 Hz:

import numpy as np
from PySeismoSoil.class_Vs_profile import Vs_Profile

print(np.floor_divide(30.0, 0.05))  # 599.0  (expected 600.0)

prof = Vs_Profile(np.array([[10.0, 0.0], [200.0, 1000.0]]).T)
for fmax, freq_resolution in [(30.0, 0.05), (30.0, 0.1), (10.0, 0.1), (20.0, 0.2), (15.0, 0.5)]:
    af_RO = prof.get_ampl_function(fmax=fmax, freq_resolution=freq_resolution)[0]
    freq = af_RO.amplitude_2col[:, 0]
    print(fmax, freq_resolution, len(freq), round(freq[-1], 6))
# 30.0 0.05 599 29.95
# 30.0 0.1 299 29.9
# 10.0 0.1 99 9.9
# 20.0 0.2 99 19.8
# 15.0 0.5 30 15.0

test_get_amplif_function() uses fmax=15 and freq_resolution=0.5, which divide exactly, so it does not catch this.

Fix

1. Use true division with a small tolerance, then round down:

   TF_size = int(np.floor(fmax / freq_resolution + 1e-6))

   A plain int(fmax / freq_resolution) is not enough, because the quotient can also land just below a whole number (0.3 / 0.1 is 2.9999999999999996). With only this change on main, the repro gives 600, 300, 100, 100 and 30 points, each ending at fmax, and all 240 tests pass. linear_site_resp() also calls linear_tf(); the tests that run it (tests/test_helper_simulations.py, and Linear_Simulation in tests/test_class_simulation.py) still pass.

2. Add a test that Vs_Profile.get_ampl_function() with the defaults returns 600 frequencies ending at 30.0, and that fmax=10, freq_resolution=0.1 returns 100 frequencies ending at 10.0.