first attempt at a general triangulation algorithm

tc/include/tc/groups.h

@@ -28,6 +28,10 @@ namespace tc {
         [[nodiscard]] Group product(const Group &other) const;
 
         [[nodiscard]] Group power(int p) const;
+
+        [[nodiscard]] Group shrink(const std::vector<int> &gens) const;
+
+        [[nodiscard]] bool trivial() const;
     };
 
     Group operator*(const Group &g, const Group &h);

tc/src/groups.cpp

@@ -66,6 +66,35 @@ namespace tc {
         return g;
     }
 
+    Group Group::shrink(const std::vector<int> &gens) const {
+        Group g(ngens);
+        for (const auto &i : gens) {
+            for (const auto &j : gens) {
+                g._mults[i][j] = _mults[i][j];
+            }
+        }
+
+        std::stringstream ss;
+        ss << name << "{";
+        for (auto e : gens) ss << " " << e;
+        ss << " }";
+        g.name = ss.str();
+
+        return g;
+    }
+
+    bool Group::trivial() const {
+        for (int i = 0; i < ngens; ++i) {
+            for (int j = 0; j < ngens; ++j) {
+                if (_mults[i][j] != 2) {
+                    return false;
+                }
+            }
+        }
+
+        return true;
+    }
+
     Group operator*(const Group &g, const Group &h) {
         return g.product(h);
     }