🔧 Define the operation -(::Quaternion)

The operation `-q` was returning an array instead of a Quaternion.

Author: ronisbr

src/quaternion.jl

@@ -118,6 +118,14 @@ Compute `qu + q` or `q + qu`, in which `qu` is the scaled identity quaternion
 # Operation: -
 # ==============================================================================
 
+"""
+    -(q::Quaternion)
+
+Return the quaterion `-q`.
+
+"""
+@inline -(q::Quaternion) = -1*q
+
 """
     -(qa::Quaternion, qb::Quaternion)
 

test/test_quaternions.jl

@@ -207,6 +207,9 @@ end
 # ====================================
 
 let
+    q = Quaternion(randn(4))
+    @test -q === -1*q
+
     q = Quaternion(1,1,1,1)
     @test typeof(q) == Quaternion{Int}