/**
Generates the
*/
std::vector<std::pair<Indices, Indices>> GenerateTwoPartition(const Indices& indices) const {
assert(indices.Size() > 1);
std::vector<std::pair<Indices, Indices>> result;
// Take the first letter
auto first = indices[0];
for (int i=1; i<indices.Size(); i++) {
auto current = indices[i];
Indices remaining = indices;
Indices gamma;
gamma.Insert(first);
gamma.Insert(current);
remaining.Remove(i);
remaining.Remove(0);
result.push_back({ gamma, remaining });
}
return result;
}
Tensor::Tensor Generate(const Indices& indices) const {
// Expect all the ranges to be in space
unsigned order = indices.Size();
for (auto& index : indices) {
if (index.GetRange() != Common::Range(1,3)) {
// throw error
}
}
// We cannot build anything with one index!
if (indices.Size() == 1) return Tensor::Tensor::Zero();
Tensor::Tensor result = Tensor::Tensor::Zero();
unsigned variableCounter = 0;
// Calculate
unsigned numEpsilon = (indices.Size() % 2 == 0) ? 0 : 1;
unsigned numGammas = (indices.Size() % 2 == 0) ? indices.Size()/2 : (indices.Size()-3)/2;
std::vector<Indices> possibleIndices;
if (numEpsilon == 1) {
possibleIndices = GenerateOddRank(indices);
} else {
possibleIndices = GenerateEvenRank(indices);
}
std::vector<Tensor::Tensor> tensors;
for (auto& newIndices : possibleIndices) {
// Create variable
Tensor::Scalar variable ("e", ++variableCounter);
tensors.push_back(variable * Tensor::Tensor::EpsilonGamma(numEpsilon, numGammas, newIndices));
}
return Tensor::Tensor::Add(tensors);
}
std::vector<Indices> GenerateEvenRank(const Indices& indices) const {
auto res = GenerateTwoPartition(indices);
std::vector<Indices> result;
if (indices.Size() == 2) {
for (auto& pair : res) {
result.push_back(pair.first);
}
} else {
for (auto& pair : res) {
auto newComb = GenerateEvenRank(pair.second);
for (auto &v : newComb) {
auto current = pair.first;
current.Append(v);
result.push_back(current);
}
}
}
return result;
}