Added structure for diff model.

src/observation/gaussian.rs

@@ -0,0 +1,36 @@
+use crate::storage::Storage;
+
+use super::Observation;
+
+pub struct GaussianObservation {
+    m: usize,
+    items: Vec<usize>,
+    coeffs: Vec<f64>,
+    indices: Vec<usize>,
+    ns_cav: Vec<f64>,
+    xs_cav: Vec<f64>,
+    t: f64,
+    logpart: f64,
+    exp_ll: usize,
+    margin: f64,
+}
+
+impl GaussianObservation {
+    pub fn new(storage: &mut Storage, elems: &[(usize, f64)], diff: f64, t: f64, var: f64) -> Self {
+        unimplemented!();
+    }
+}
+
+impl Observation for GaussianObservation {
+    fn match_moments(&self, mean_cav: f64, cov_cav: f64) -> (f64, f64, f64) {
+        unimplemented!();
+    }
+
+    fn ep_update(&mut self, lr: f64, storage: &mut Storage) -> f64 {
+        unimplemented!();
+    }
+
+    fn kl_update(&mut self, lr: f64, storage: &mut Storage) -> f64 {
+        unimplemented!();
+    }
+}