Math: reverse scalar/quaternion multiplication and division operators.

Also updated related documentation in RectangularMatrix.

src/Math/Quaternion.h

@@ -257,6 +257,27 @@ template<class T> class Quaternion {
         T _scalar;
 };
 
+/** @relates Quaternion
+@brief Multiply scalar with quaternion
+
+Same as Quaternion::operator*(T) const.
+*/
+template<class T> inline Quaternion<T> operator*(T scalar, const Quaternion<T>& quaternion) {
+    return quaternion*scalar;
+}
+
+/** @relates Quaternion
+@brief Divide quaternion with number and invert
+
+@f[
+    \frac a q = [\frac a {\boldsymbol q_V}, \frac a {q_S}]
+@f]
+@see Quaternion::operator/()
+*/
+template<class T> inline Quaternion<T> operator/(T scalar, const Quaternion<T>& quaternion) {
+    return {scalar/quaternion.vector(), scalar/quaternion.scalar()};
+}
+
 /** @debugoperator{Magnum::Math::Geometry::Rectangle} */
 template<class T> Corrade::Utility::Debug operator<<(Corrade::Utility::Debug debug, const Quaternion<T>& value) {
     debug << "Quaternion({";

src/Math/RectangularMatrix.h

@@ -385,7 +385,7 @@ template<std::size_t cols, std::size_t rows, class T> class RectangularMatrix {
 /** @relates RectangularMatrix
 @brief Multiply number with matrix
 
-@see RectangularMatrix::operator*(U) const
+Same as RectangularMatrix::operator*(U) const.
 */
 #ifndef DOXYGEN_GENERATING_OUTPUT
 template<std::size_t cols, std::size_t rows, class T, class U> inline typename std::enable_if<std::is_arithmetic<U>::value, RectangularMatrix<cols, rows, T>>::type operator*(U number, const RectangularMatrix<cols, rows, T>& matrix) {
@@ -398,11 +398,9 @@ template<std::size_t cols, std::size_t rows, class T, class U> inline Rectangula
 /** @relates RectangularMatrix
 @brief Divide matrix with number and invert
 
-Example:
+@f[
-@code
+    \boldsymbol B_{ji} = \frac a {\boldsymbol A_{ji}}
-RectangularMatrix<2, 3, float> mat(1.0f, 2.0f, -4.0f, 8.0f, -1.0f, 0.5f);
+@f]
-RectangularMatrix<2, 3, float> another = 1.0f/mat; // {1.0f, 0.5f, -0.25f, 0.128f, -1.0f, 2.0f}
-@endcode
 @see RectangularMatrix::operator/()
 */
 #ifndef DOXYGEN_GENERATING_OUTPUT

src/Math/Test/MathQuaternionTest.cpp

@@ -76,7 +76,10 @@ void QuaternionTest::multiplyDivideScalar() {
     Quaternion b({-1.5f, -4.5f, 3.0f}, 6.0f);
 
     CORRADE_COMPARE(a*-1.5f, b);
+    CORRADE_COMPARE(-1.5f*a, b);
     CORRADE_COMPARE(b/-1.5f, a);
+
+    CORRADE_COMPARE(2.0f/a, Quaternion({2.0f, 0.666666f, -1.0f}, -0.5f));
 }
 
 void QuaternionTest::multiply() {