Make tc::Group an Eigen::Matrix (Schafli Matrix)

Makes tc::Group a direct subclass of Eigen::Matrix. Group should represent a Schlafli matrix.

Added a note that tc::solve assumes the matrix to be for a coxeter group.

In theory we could also implement the "normal" todd-coxeter and allow any Schlafli matrix as input.

example/bench.cpp

@@ -15,7 +15,7 @@ void test(const G &group) {
     int order = cosets.order();
 
     std::cout
-        << std::setw(7) << group.name() << ", "
+        << std::setw(7) << group.name << ", "
         << std::setw(7) << order << ", "
         << std::fixed << std::setprecision(6) << diff << "s"
         << std::endl;

include/tc/core/group.hpp

@@ -10,81 +10,59 @@
 #include <Eigen/Eigen>
 #include <iostream>
 
+namespace {
+    template<class T>
+    std::string stringify(const T &vec) {
+        std::stringstream ss;
+        ss << "[" << vec << "]";
+        return ss.str();
+    }
+}
+
 namespace tc {
+    /// A Schlafli Matrix
     template<unsigned int Rank>
-    struct Group;
-
-    template<unsigned int Rank, unsigned int PRank>
-    struct SubGroup;
-
-    template<unsigned int Rank>
-    class Group {
+    class Group : public Eigen::Matrix<unsigned int, Rank, Rank> {
     public:
-        using Matrix = Eigen::Matrix<unsigned int, Rank, Rank>;
+        using Base = Eigen::Matrix<unsigned int, Rank, Rank>;
 
-    private:
-    public:
-        std::string _name;
-        Matrix _data;
-        Eigen::SelfAdjointView<Matrix, Eigen::Upper> _mults;
+        std::string name;
 
-    public:
-        Group(const Group<Rank> &g) :
-            _name(g._name),
-            _data(g._data),
-            _mults(_data) {
-        }
-
-        Group(Group &&g) noexcept:
-            _name(std::move(g._name)),
-            _data(std::move(g._data)),
-            _mults(_data) {
-        }
-
-        explicit Group(std::string name = "G") :
-            _name(std::move(name)),
-            _data(),
-            _mults(_data) {
-            _data.fill(2);
-        }
-
-        unsigned int rank() const {
-            return _data.rows();
-        }
-
-        std::string name() const {
-            return _name;
-        }
-
-        typename Matrix::Scalar &operator()(int a, int b) {
-            return _mults(a, b);
-        }
-
-        typename Matrix::Scalar operator()(int a, int b) const {
-            return _mults(a, b);
-        }
+        using Base::Base;
     };
 
+    template<unsigned int Rank>
+    using Symbol = Eigen::Vector<unsigned int, Rank>;
+
+    template<unsigned int Rank>
+    Group<Rank> schlafli(const Symbol<Rank - 1> &mults, const std::string &name) {
+        Group<Rank> res;
+        res.name = name;
+
+        res.fill(2);
+        res.topRightCorner(Rank - 1, Rank - 1).diagonal() << mults;
+        res.bottomLeftCorner(Rank - 1, Rank - 1).diagonal() << mults;
+
+        return res;
+    }
+
+    template<unsigned int Rank>
+    Group<Rank> schlafli(const Symbol<Rank - 1> &mults) {
+        return schlafli<Rank>(mults, stringify(mults));
+    }
+
     template<unsigned int GR, unsigned int HR>
     Group<GR + HR> product(const Group<GR> &g, const Group<HR> &h) {
-        std::stringstream ss;
-        ss << g.name << "*" << h.name;
+        Group<GR + HR> res;
+        res.name = g.name + "*" + h.name;
 
-        Group<GR + HR> res(ss.str());
+        res.fill(2);
 
         int off = 0;
-        for (int i = 0; i < GR; ++i) {
-            for (int j = i; j < GR; ++j) {
-                res(i + off, j + off) = g(i, j);
-            }
-        }
+        res.block(off, off, GR, GR) << g.array() + off;
         off += GR;
 
-        for (int i = 0; i < HR; ++i) {
-            for (int j = i; j < HR; ++j) {
-                res(i + off, j + off) = h(i, j);
-            }
-        }
+        res.block(off, off, HR, HR) << h.array() + off;
         off += HR;
 
         return res;
@@ -92,19 +70,14 @@ namespace tc {
 
     template<unsigned int GR, unsigned int P>
     Group<GR * P> power(const Group<GR> &g) {
-        std::stringstream ss;
-        ss << g.name << "^" << P;
+        Group<GR * P> res;
+        res.name = g.name + "^" + P;
 
-        Group<GR * P> res(ss.str());
+        res.fill(2);
 
         for (int k = 0; k < P; ++k) {
             int off = k * GR;
-
-            for (int i = 0; i < GR; ++i) {
-                for (int j = i; j < GR; ++j) {
-                    res(i + off, j + off) = g(i, j);
-                }
-            }
+            res.block(off, off, GR, GR) << g.array() + off;
         }
 
         return res;

include/tc/core/solver.hpp

@@ -242,8 +242,11 @@ namespace {
 }
 
 namespace tc {
+    /**
+     * Assumes that g is a coxeter group - that is, self-adjoint and the diagonal is 2.
+     */
     template<unsigned int Rank>
-    tc::Cosets<Rank> solve(const Group <Rank> &g, const std::vector<int> &sub_gens = {}) {
+    tc::Cosets<Rank> solve(const Group <Rank> &group, const std::vector<int> &sub_gens = {}) {
         tc::Cosets<Rank> cosets;
         cosets.add_row();
 
@@ -256,7 +259,7 @@ namespace tc {
                 cosets.put(0, gen, 0);
         }
 
-        Tables<Rank> tables(g);
+        Tables<Rank> tables(group);
         tables.add_row();
         tables.initialize(0, cosets);
 

include/tc/groups.hpp

@@ -2,167 +2,150 @@
 
 #include "core.hpp"
 
-namespace tc {
+namespace tc::group {
     /**
-     * Construct a group from a (simplified) Schlafli Symbol of the form [a, b, ..., c]
-     * @param mults: The sequence of multiplicites between adjacent generators.
+     * Universal Coxeter Group
      */
     template<unsigned int Rank>
-    Group <Rank> schlafli(const std::array<unsigned int, Rank - 1> &mults, const std::string &name) {
-        Group<Rank> g(name);
+    Group <Rank> U() {
+        std::stringstream ss;
+        ss << "U(" << Rank << ")";
 
-        for (int i = 0; i < Rank - 1; i++) {
-            g(i, i + 1) = mults[i];
+        Group<Rank> res;
+        res.name = ss.str();
+        res.fill(2);
+        return res;
+    }
+
+    /**
+     * Simplex
+     */
+    template<unsigned int Rank>
+    Group <Rank> A() {
+        std::stringstream ss;
+        ss << "A(" << Rank << ")";
+
+        if (Rank == 0) {
+            Group<Rank> res;
+            res.name = ss.str();
+            return res;
         }
 
+        std::array<unsigned int, Rank - 1> mults;
+        mults.fill(3);
+
+        return schlafli<Rank>(mults, ss.str());
+    }
+
+    /**
+     * Cube, Orthoplex
+     */
+    template<unsigned int Rank>
+    Group <Rank> B() {
+        std::stringstream ss;
+        ss << "B(" << Rank << ")";
+
+        tc::Symbol<Rank - 1> mults;
+        mults.fill(3);
+        mults(0) = 4;
+
+        return schlafli<Rank>(mults, ss.str());
+    }
+
+    /**
+     * Demicube, Orthoplex
+     */
+    template<unsigned int Rank>
+    Group <Rank> D() {
+        std::stringstream ss;
+        ss << "D(" << Rank << ")";
+
+        tc::Symbol<Rank - 1> mults;
+        mults.fill(3);
+        mults(Rank - 2) = 2;
+
+        Group<Rank> g = schlafli<Rank>(mults, ss.str());
+        g(1, Rank - 1) = 3;
+        g(Rank - 1, 1) = 3;
+
         return g;
     }
 
     /**
-     * Construct a group from a (simplified) Schlafli Symbol of the form [a, b, ..., c]
-     * @param mults: The sequence of multiplicites between adjacent generators.
+     * E groups
      */
     template<unsigned int Rank>
-    Group <Rank> schlafli(const std::array<unsigned int, Rank - 1> &mults) {
+    Group <Rank> E() {
         std::stringstream ss;
-        ss << "[";
-        if (Rank) {
-            for (size_t i = 0; i < Rank - 2; ++i) {
-                ss << mults[i] << ",";
-            }
-            ss << mults[Rank - 1];
-        }
-        ss << "]";
+        ss << "E(" << Rank << ")";
+
+        tc::Symbol<Rank - 1> mults;
+        mults.fill(3);
+        mults(Rank - 2) = 2;
+
+        Group<Rank> g = schlafli<Rank>(mults, ss.str());
+        g(2, Rank - 1) = 3;
+        g(Rank - 1, 2) = 3;
+
+        return g;
+    }
+
+    /**
+     * 24 Cell
+     */
+    Group<4> F4() {
+        return schlafli<4>({3, 4, 3}, "F4");
+    }
+
+    /**
+     * Hexagon
+     */
+    Group<2> G2() {
+        return schlafli<2>(tc::Symbol<1>(6), "G2");
+    }
+
+    /**
+     * Icosahedron
+     */
+    template<unsigned int Rank>
+    Group <Rank> H() {
+        std::stringstream ss;
+        ss << "H(" << Rank << ")";
+
+        tc::Symbol<Rank - 1> mults;
+        mults.fill(3);
+        mults(0) = 5;
 
         return schlafli<Rank>(mults, ss.str());
     }
 
-    namespace group {
-        /**
-         * Simplex
-         */
-        template<unsigned int Rank>
-        Group <Rank> A() {
-            std::stringstream ss;
-            ss << "A(" << Rank << ")";
+    /**
+     * Polygonal
+     */
+    Group<2> I2(unsigned int n) {
+        std::stringstream ss;
+        ss << "I2(" << n << ")";
 
-            if (Rank == 0)
-                return Group<Rank>(ss.str());
+        return schlafli<2>(tc::Symbol<1>(n), ss.str());
+    }
 
-            std::array<unsigned int, Rank - 1> mults;
-            mults.fill(3);
+    /**
+     * Toroidal. I2(n) * I2(m)
+     */
+    Group<4> T(unsigned int n, unsigned int m) {
+        std::stringstream ss;
+        ss << "T(" << n << "," << m << ")";
 
-            return schlafli<Rank>(mults, ss.str());
-        }
+        return schlafli<4>({n, 2, m}, ss.str());
+    }
 
-        /**
-         * Cube, Orthoplex
-         */
-        template<unsigned int Rank>
-        Group <Rank> B() {
-            std::stringstream ss;
-            ss << "B(" << Rank << ")";
+    /**
+     * Toroidal. T(n, n)
+     */
+    Group<4> T(unsigned int n) {
+        std::stringstream ss;
+        ss << "T(" << n << ")";
 
-            std::array<unsigned int, Rank - 1> mults;
-            mults.fill(3);
-            mults[0] = 4;
-
-            return schlafli<Rank>(mults, ss.str());
-        }
-
-        /**
-         * Demicube, Orthoplex
-         */
-        template<unsigned int Rank>
-        Group <Rank> D() {
-            std::stringstream ss;
-            ss << "D(" << Rank << ")";
-
-            std::array<unsigned int, Rank - 1> mults;
-            mults.fill(3);
-            mults[Rank - 2] = 2;
-
-            Group<Rank> g = schlafli<Rank>(mults, ss.str());
-            g(1, Rank - 1) = 3;
-
-            return g;
-        }
-
-        /**
-         * E groups
-         */
-        template<unsigned int Rank>
-        Group <Rank> E() {
-            std::stringstream ss;
-            ss << "E(" << Rank << ")";
-
-            std::array<unsigned int, Rank - 1> mults;
-            mults.fill(3);
-            mults[Rank - 2] = 2;
-
-            Group<Rank> g = schlafli<Rank>(mults, ss.str());
-            g(2, Rank - 1) = 3;
-
-            return g;
-        }
-
-        /**
-         * 24 Cell
-         */
-        Group<4> F4() {
-            return schlafli<4>({3, 4, 3}, "F4");
-        }
-
-        /**
-         * Hexagon
-         */
-        Group<2> G2() {
-            return schlafli<2>({6}, "G2");
-        }
-
-        /**
-         * Icosahedron
-         */
-        template<unsigned int Rank>
-        Group <Rank> H() {
-            std::stringstream ss;
-            ss << "H(" << Rank << ")";
-
-            std::array<unsigned int, Rank - 1> mults;
-            mults.fill(3);
-            mults[0] = 5;
-
-            return schlafli<Rank>(mults, ss.str());
-        }
-
-        /**
-         * Polygonal
-         */
-        Group<2> I2(unsigned int n) {
-            std::stringstream ss;
-            ss << "I2(" << n << ")";
-
-            return schlafli<2>({n}, ss.str());
-        }
-
-        /**
-         * Toroidal. I2(n) * I2(m)
-         */
-        Group<4> T(unsigned int n, unsigned int m) {
-            std::stringstream ss;
-            ss << "T(" << n << "," << m << ")";
-
-            return schlafli<4>({n, 2, m}, ss.str());
-        }
-
-        /**
-         * Toroidal. T(n, n)
-         */
-        Group<4> T(unsigned int n) {
-            std::stringstream ss;
-            ss << "T(" << n << ")";
-
-            return schlafli<4>({n, 2, n}, ss.str());
-        }
+        return schlafli<4>({n, 2, n}, ss.str());
     }
 }