--- a/src/discrete.rs	Fri Jan 16 14:09:45 2026 -0500
+++ b/src/discrete.rs	Sat Jan 24 19:24:29 2026 -0500
@@ -137,6 +137,12 @@
     //     self.spikes.iter_mut().zip(iter).for_each(|(δ, v)| δ.set_mass(g(δ.get_mass(), v)));
     // }
 
+    /// Truncate to `len`.
+    #[inline]
+    pub fn truncate(&mut self, len: usize) {
+        self.spikes.truncate(len);
+    }
+
     /// Prune all spikes with zero mass.
     #[inline]
     pub fn prune(&mut self) {