Division by 0 error in FastFitter

[weiliangjin2021]

The code to reproduce the error:

import numpy as np
from tidy3d.plugins.dispersion import FastDispersionFitter

N = 2
wvl_um = np.linspace(0.5, 0.6, N)
n_data = np.ones(N) * 2
k_data = np.ones(N) * 0.5

fitter = FastDispersionFitter(wvl_um = wvl_um, n_data = n_data, k_data = k_data)
medium, rms_error = fitter.fit(max_num_poles=2, tolerance_rms=1e-3)

Error message:

tidy3d_frontend/tidy3d/plugins/dispersion/fit_fast.py:360: RuntimeWarning: divide by zero encountered in divide
pole_matrix[:, offset + 2 * i] = 1 / (1j * omega + pole) + 1 / (
File "tidy3d_frontend/tidy3d/plugins/dispersion/fit_fast.py", line 498, in fit_residues
x_vector = scipy.optimize.lsq_linear(a_matrix_real, b_vector_real).x
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "python3.11/site-packages/scipy/optimize/_lsq/lsq_linear.py", line 316, in lsq_linear
unbd_lsq = np.linalg.lstsq(A, b, rcond=-1)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "python3.11/site-packages/numpy/linalg/linalg.py", line 2326, in lstsq
x, resids, rank, s = gufunc(a, b, rcond, signature=signature, extobj=extobj)
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
File "python3.11/site-packages/numpy/linalg/linalg.py", line 124, in _raise_linalgerror_lstsq
raise LinAlgError("SVD did not converge in Linear Least Squares")
numpy.linalg.LinAlgError: SVD did not converge in Linear Least Squares