From 00621521206e507df05d2470cb55fd54595ea610 Mon Sep 17 00:00:00 2001
From: dellaert <dellaert@cc.gatech.edu>
Date: Sat, 23 May 2015 22:00:39 -0700
Subject: [PATCH] prototyping direct sum

---
 gtsam/geometry/tests/testCyclic.cpp | 90 ++++++++++++++++++++++++++++-
 1 file changed, 89 insertions(+), 1 deletion(-)

diff --git a/gtsam/geometry/tests/testCyclic.cpp b/gtsam/geometry/tests/testCyclic.cpp
index a15d7e2c2..eaacea5c3 100644
--- a/gtsam/geometry/tests/testCyclic.cpp
+++ b/gtsam/geometry/tests/testCyclic.cpp
@@ -58,18 +58,106 @@ TEST(Cyclic, Between) {
 }
 
 //******************************************************************************
-TEST(Cyclic, Ivnverse) {
+TEST(Cyclic, Inverse) {
   EXPECT_LONGS_EQUAL(0, traits<G>::Inverse(G(0)));
   EXPECT_LONGS_EQUAL(2, traits<G>::Inverse(G(1)));
   EXPECT_LONGS_EQUAL(1, traits<G>::Inverse(G(2)));
 }
 
+//******************************************************************************
+TEST(Cyclic, Negation) {
+  EXPECT_LONGS_EQUAL(0, -G(0));
+  EXPECT_LONGS_EQUAL(2, -G(1));
+  EXPECT_LONGS_EQUAL(1, -G(2));
+}
+
+//******************************************************************************
+TEST(Cyclic, Negation2) {
+  typedef Cyclic<2> Z2;
+  EXPECT_LONGS_EQUAL(0, -Z2(0));
+  EXPECT_LONGS_EQUAL(1, -Z2(1));
+}
+
 //******************************************************************************
 TEST(Cyclic , Invariants) {
   G g(2), h(1);
  check_group_invariants(g,h);
 }
 
+//******************************************************************************
+namespace gtsam {
+
+template<typename G, typename H>
+class DirectSum: public std::pair<G, H> {
+  BOOST_CONCEPT_ASSERT((IsGroup<G>));  // TODO(frank): check additive
+  BOOST_CONCEPT_ASSERT((IsGroup<H>));  // TODO(frank): check additive
+  BOOST_CONCEPT_ASSERT((IsTestable<G>));
+  BOOST_CONCEPT_ASSERT((IsTestable<H>));
+
+  const G& g() const { return this->first; }
+  const H& h() const { return this->second;}
+
+public:
+  // Construct from two subgroup elements
+  DirectSum(const G& g, const H& h):std::pair<G,H>(g,h) {}
+
+  /// Default constructor yields identity
+  DirectSum():std::pair<G,H>(G::Identity(),H::Identity()) {
+  }
+
+  /// Identity element
+  static DirectSum Identity() {
+    return DirectSum();
+  }
+  /// Addition
+  DirectSum operator+(const DirectSum& other) const {
+    return DirectSum(g()+other.g(), h()+other.h());
+  }
+  /// Subtraction
+  DirectSum operator-(const DirectSum& other) const {
+    return DirectSum(g()-other.g(), h()-other.h());
+  }
+  /// Inverse
+  DirectSum operator-() const {
+    return DirectSum(- g(), - h());
+  }
+  /// print with optional string
+  void print(const std::string& s = "") const {
+    std::cout << s << "(\n";
+    traits<G>::Print(g());
+    std::cout << ",\n";
+    traits<H>::Print(h());
+    std::cout << ")" << std::endl;
+  }
+  /// equals with an tolerance, prints out message if unequal
+  bool equals(const DirectSum& other, double tol = 1e-9) const {
+    return *this == other; // uses std::pair operator
+  }
+};
+
+/// Define direct sums to be a model of the Additive Group concept
+template<typename G, typename H>
+struct traits<DirectSum<G, H> > : internal::AdditiveGroupTraits<DirectSum<G, H> >, //
+    Testable<DirectSum<G, H> > {
+};
+
+}  // namespace gtsam
+
+TEST(Cyclic , DirectSum) {
+  // The Direct sum of Cyclic<2> and Cyclic<2> is *not* Cyclic<4>, but the
+  // smallest non-cyclic group called the Klein four-group:
+  typedef DirectSum<Cyclic<2>, Cyclic<2> > K;
+  BOOST_CONCEPT_ASSERT((IsGroup<K>));
+  BOOST_CONCEPT_ASSERT((IsTestable<K>));
+
+  K g(0, 1), h(1, 1);
+  EXPECT(assert_equal(K(0, 1), - g));
+  EXPECT(assert_equal(K(), g + g));
+  EXPECT(assert_equal(K(1, 0), g + h));
+  EXPECT(assert_equal(K(1, 0), g - h));
+  check_group_invariants(g, h);
+}
+
 //******************************************************************************
 int main() {
   TestResult tr;