Impulse Response Calculation

Hi, I'm not sure that the following is a bug or it is correct, I report what I notice: I was looking the arrivals_to_impulse_response function in uwapm.py file and its computation. I notice that the amplitude of the arrival, row.arrival_amplitude, is setted in the right ndx position for each arrival, but, because ndx is computed as an approximation of the time of arrival (ndx = int(_np.round((row.time_of_arrival.real-t0)*fs))) can be happen that 2 different arrival have the same ndx index. In this case is correct to replace the ir[ndx] value with the last arrival amplitude, or should be added the new amplitude to the previous (ir[ndx] += row.arrival_amplitude)? In the first case aren't we losing one (or more) arrival? I tried to generate arrivals with the following script:

import arlpy.uwapm as pm

fs = 10000  
env = pm.create_env2d()
rays = pm.compute_eigenrays(env, debug=True)
arrivals = pm.compute_arrivals(env)
ir = pm.arrivals_to_impulse_response(arrivals, fs, True)

Then I try to do some elaboration to investigate the results, I build two dictionary, A_arr, A_ir, which contains the pairs: time of arrival (approximated as in arrivals_to_impulse_response function) and a list of the amplitudes of each arrival received at this time. In lost_arr list is contained the tuple of "lost arrivals".

A_arr = {} # Amplitude of arrivals
A_ir  = {} # Amplitude of impulse response

for i in range(len(ir)):
    if ir[i] != 0:
        ir_T = (i/fs)
        A_ir[ir_T] = ir[i]

for _, arr in arrivals.iterrows():
    T_ = round(arr.time_of_arrival, 4)
    if T_ in A_arr.keys():
        A_arr[T_.real].append(arr.arrival_amplitude)
    else:
        A_arr[T_.real] = [arr.arrival_amplitude]

lost_arr = []
for (T, A) in A_arr.items():
    for A_ in A:
        if A_ != A_ir[T]:
            lost_arr.append((T, A_))

print(f'Lost arrivals: {lost_arr}')

I also try to plot the sum of the amplitude of the impulse response and the sum of the amplitudes of the arrival (which I expected to be the same), but they differ in the quantities present inlost_arr.

>>> print(f'Sum of arrival amplitudes: {sum(list(arrivals.arrival_amplitude))}')
>>> print(f'Sum of impulse response amplitudes: {sum(ir)}')
>>> print(f'Sum of impulse response amplitudes + lost arrivals: {sum(ir) + sum([e[1] for e in lost_arr])}')
Sum of arrival amplitudes: (0.00023585833449997007+0.001292865475452424j)
Sum of impulse response amplitudes: (-7.266767664939084e-05+0.0012367161871826558j)
Sum of impulse response amplitudes + lost arrivals: (0.00023585833449997015+0.0012928654754524244j)

I'm not sure if there is nothing wrong in my reasoning, if so I apologize, otherwise can you check too? In case it is correct to fix it replacing with ir[ndx] += row.arrival_amplitude the similar line in uwapm.arrivals_to_impulse_response function?

Thanks!

org-arl / arlpy

Impulse Response Calculation #94