add docstring and GTSAM_EXPORT for ComputeLogNormalizer

gtsam/hybrid/GaussianMixtureFactor.h

@@ -179,7 +179,16 @@ template <>
 struct traits<GaussianMixtureFactor> : public Testable<GaussianMixtureFactor> {
 };
 
-double ComputeLogNormalizer(
+/**
+ * @brief Helper function to compute the sqrt(|2πΣ|) normalizer values
+ * for a Gaussian noise model.
+ * We compute this in the log-space for numerical accuracy.
+ *
+ * @param noise_model The Gaussian noise model
+ * whose normalizer we wish to compute.
+ * @return double
+ */
+GTSAM_EXPORT double ComputeLogNormalizer(
     const noiseModel::Gaussian::shared_ptr &noise_model);
 
 }  // namespace gtsam