import numpy as np

import pandas as pd

import matplotlib.pyplot as plt

from pandas_datareader import data as web

from scipy.stats import norm

from scipy.optimize import brentq

```

def _read_fred_series(series_id, start_date, end_date):

series = web.DataReader(series_id, "fred", start_date, end_date)[series_id]

series = pd.to_numeric(series, errors="coerce").dropna().sort_index()

# Download directly from FRED's CSV endpoint. This avoids pandas-datareader,

# which is unmaintained and incompatible with pandas 3.0.

url = f"https://fred.stlouisfed.org/graph/fredgraph.csv?id={series_id}"

df = pd.read_csv(url, index_col=0, parse_dates=True)

series = pd.to_numeric(df.iloc[:, 0], errors="coerce").dropna().sort_index()

series = series.loc[start_date:end_date]

if series.empty:

raise ValueError(f"FRED series '{series_id}' returned no data in sample window")

return series