diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2cc9e3e..800fbde 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
    - add extrapolation
    - add not-a-knot boundary condition
    - add clamped boundary condition
+   - add periodic boundary condition
    - make not-a-knot boundary condition the default
    - allow any first or second derivative as boundary condition
  - fix typo `Biliniar` -> `Bilinear`
diff --git a/Cargo.toml b/Cargo.toml
index 18360ac..2a78ec9 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -1,6 +1,6 @@
 [package]
 name = "ndarray-interp"
-version = "0.4.1"
+version = "0.5.0"
 edition = "2021"
 license = "MIT"
 description = "Interpolation package for ndarray"
@@ -13,7 +13,7 @@ categories = ["science", "algorithms", "mathematics"]
 
 [dependencies]
 ndarray = "0.15"
-num-traits = {version = "0.2"}
+num-traits = "0.2"
 thiserror = "1.0"
 
 [dev-dependencies]
diff --git a/src/interp1d/strategies/cubic_spline.rs b/src/interp1d/strategies/cubic_spline.rs
index 849bcc5..7a4f0a2 100644
--- a/src/interp1d/strategies/cubic_spline.rs
+++ b/src/interp1d/strategies/cubic_spline.rs
@@ -15,6 +15,9 @@ use super::{Interp1DStrategy, Interp1DStrategyBuilder};
 
 const AX0: Axis = Axis(0);
 
+/// Marker trait that is implemented for anithing that satisfies
+/// the trait bounds required to be used as an element in the QubicSpline
+/// strategy.
 pub trait SplineNum:
     Debug
     + Num