Math: complex number multiplication.

src/Math/Complex.h

@@ -171,6 +171,18 @@ template<class T> class Complex {
             return Complex<T>(*this) /= scalar;
         }
 
+        /**
+         * @brief Multiply with complex number
+         *
+         * @f[
+         *      c_0 c_1 = (a_0 + ib_0)(a_1 + ib_1) = (a_0 a_1 - b_0 b_1) + i(a_1 b_0 + a_0 b_1)
+         * @f]
+         */
+        inline Complex<T> operator*(const Complex<T>& other) const {
+            return {_real*other._real - _imaginary*other._imaginary,
+                    _imaginary*other._real + _real*other._imaginary};
+        }
+
     private:
         T _real, _imaginary;
 };

src/Math/Test/ComplexTest.cpp

@@ -33,6 +33,7 @@ class ComplexTest: public Corrade::TestSuite::Tester {
         void addSubtract();
         void negated();
         void multiplyDivideScalar();
+        void multiply();
 
         void debug();
 };
@@ -47,6 +48,7 @@ ComplexTest::ComplexTest() {
              &ComplexTest::addSubtract,
              &ComplexTest::negated,
              &ComplexTest::multiplyDivideScalar,
+             &ComplexTest::multiply,
 
              &ComplexTest::debug);
 }
@@ -117,6 +119,15 @@ void ComplexTest::multiplyDivideScalar() {
     CORRADE_COMPARE(-2.0f/a, c);
 }
 
+void ComplexTest::multiply() {
+    Complex a( 5.0f,   3.0f);
+    Complex b( 6.0f,  -7.0f);
+    Complex c(51.0f, -17.0f);
+
+    CORRADE_COMPARE(a*b, c);
+    CORRADE_COMPARE(b*a, c);
+}
+
 void ComplexTest::debug() {
     std::ostringstream o;