small fix

Author: vegard-solum-4ss

src/smsfusion/_smoothing.py

@@ -42,6 +42,7 @@ def __init__(self, ains: AidedINS | AHRS | VRU, cov_smoothing: bool = True) -> N
         self._ains = ains
         self._cov_smoothing = cov_smoothing
 
+        # Buffers for storing state and covariance estimates from forward sweep
         self._x_buf = []  # state estimates (w/o smoothing)
         self._P_buf = []  # error covariance estimates (w/o smoothing)
         self._dx_buf = []  # error-state estimates (w/o smoothing)
@@ -50,6 +51,10 @@ def __init__(self, ains: AidedINS | AHRS | VRU, cov_smoothing: bool = True) -> N
         self._x = np.array([])  # smoothed state estimates
         self._P = np.array([])  # smoothed error covariance estimate
 
+        # Smoothed state and covariance estimates
+        self._x = np.empty((0, 16), dtype="float64")
+        self._P = np.empty((0, *self._ains.P.shape), dtype="float64")
+
     @property
     def ains(self) -> AidedINS | AHRS | VRU:
         """