Indexing fix in CTA calculation (#31)

Author: fsoubelet

optics_functions/__init__.py

@@ -5,7 +5,7 @@
 __title__ = "optics_functions"
 __description__ = "Calculate optics parameters from TWISS outputs."
 __url__ = "https://github.com/pylhc/optics_functions"
-__version__ = "0.1.1"
+__version__ = "0.1.2"
 __author__ = "pylhc"
 __author_email__ = "[email protected]"
 __license__ = "MIT"

optics_functions/coupling.py

@@ -341,7 +341,7 @@ def _get_weights_from_lengths(df: TfsDataFrame) -> Tuple[float, np.array]:
     # approximate length of each element (ds in integral)
     s_periodic = np.zeros(len(df) + 1)
     s_periodic[1:] = df[S].to_numpy()
-    s_periodic[0] = df[S][-1] - df.headers[LENGTH]
+    s_periodic[0] = df[S].to_numpy()[-1] - df.headers[LENGTH]
 
     # weight ds/(2*pi*R) * N (as we take the mean afterwards)
     weights = np.diff(s_periodic) / df.headers[LENGTH] * len(df)