fix lotka volterra

Author: arrjon

bayesflow/simulators/benchmark_simulators/lotka_volterra.py

@@ -114,7 +114,7 @@ def observation_model(self, params: np.ndarray) -> np.ndarray:
         pp = np.clip(pp, a_min=1e-10, a_max=10000.0)
 
         # Add noise, decide whether to flatten and return
-        x = self.rng.lognormal(pp, sigma=self.obs_noise)
+        x = self.rng.lognormal(np.log(pp), sigma=self.obs_noise)
         if self.flatten:
             return x.flatten()
         return x