Added a branchlength move

src/branchlength.rs

@@ -1,9 +1,40 @@
 use crate::{rate_matrix::RateMatrix, treestate::TreeMove};
-
-pub struct BranchMove{}
+use rand::prelude::Distribution;
+// use rand::distributions::Normal;
+use statrs::distribution::Normal;
+use crate::topology::Topology;
+use crate::TreeState;
+pub struct BranchMove{
+    indices: Vec<usize>,
+}
 
 impl<R: RateMatrix> TreeMove<R> for BranchMove {
     fn generate(&self, ts: &crate::treestate::TreeState<R>) -> crate::treestate::TreeState<R> {
-        todo!()
+        let normal = Normal::new(0.0, 1.0).unwrap();
+        let mut changes: Vec<usize> = Vec::new();
+
+        // This is not ideal
+        let mut nodes = ts.top.nodes.clone();
+
+        for i in self.indices.iter() {
+            let ind = *i;
+            let mut bl = nodes[ind].get_branchlen();
+            bl = bl.ln() + normal.sample(&mut rand::thread_rng());
+            nodes[ind].set_branchlen(bl.exp());
+            changes.push(ind);
+        }
+
+        let new_top = Topology{
+            nodes: nodes,
+            tree_vec: ts.top.tree_vec.clone(),
+            likelihood: ts.top.likelihood,
+        };
+
+        TreeState{
+            top: new_top,
+            mat: ts.mat,
+            ll: ts.ll,
+            changed_nodes: Some(changes),
+        }
     }
 }