Fix changelog and method derivative() in class Quaternion.

CHANGELOG.md

@@ -1,26 +1,38 @@
 # Changelog
+
 All notable changes to this project will be documented in this file.
 
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [0.2.2] - 2020-01-06
 ### Added
-- This changelog
+- This changelog.
 - Script `triad.py` for future submodule implementation of TRIAD method.
 
 ### Changed
 - Action `Build Python Package` builds **only** when new commit is pushed to `master` branch.
 - Simplify building triads in function `triad` of submodule `orientation`.
 - Fix documentation of `am2angles` and `quest` of submodule `orientation`.
 
-
 ## [0.2.1] - 2020-01-06
 ### Added
-- Action `Build Python Package` to build when new commit is pushed.
-- Script `triad.py` for future submodule implementation of TRIAD method.
+- Class `QuaternionArray` to handle several quaternions at once.
+- Add methods `log()`, `exp()`, `inv()`, `to_array()` and `to_list()` to class `Quaternion`.
 
 ### Changed
-- Action `Build Python Package` builds **only** when new commit is pushed to `master` branch.
-- Simplify building triads in function `triad` of submodule `orientation`.
-- Fix documentation of `am2angles` and `quest` of submodule `orientation`.
+- Fix and/or improve 
+
+## [0.2.0] - 2019-12-27
+### Added
+- Class `Quaternion` to handle quaternion operations.
+- Add methods `log()`, `exp()`, `inv()`, `to_array()` and `to_list()` to class `Quaternion`.
+- More definitions of colors with formats ints and floats.
+- Functions `hex_to_int()` and `hex_to_float()` convert any color defined as hex into `int` and `float`.
+- Badges in README to indicate basic information.
+
+### Changed
+- Improve versioning.
+
+### Removed
+- Function `R2q()` to get quaternion from rotation matrix. Method `from_DCM()` of class `Quaternion` is preferred.

ahrs/common/quaternion.py

@@ -1163,17 +1163,16 @@ def derivative(self, w):
         Returns
         -------
         dq/dt : array
-            Derivative of quaternion.
+            Derivative of quaternion
 
         """
         if w.ndim != 1 or w.shape[0] != 3:
             raise ValueError("Expected `w` to have shape (3,), got {}.".format(w.shape))
-        w = np.concatenate(([0.0], w))
         F = 0.5*np.array([
             [0.0, -w[0], -w[1], -w[2]],
-            [w[0], 0.0, w[2], -w[1]],
-            [w[1], -w[2], 0.0, w[0]],
-            [w[2], w[1], -w[0], 0.0]])
+            [w[0], 0.0, -w[2], w[1]],
+            [w[1], w[2], 0.0, -w[0]],
+            [w[2], -w[1], w[0], 0.0]])
         return F@self.q
 
 class QuaternionArray: