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	diff --git a/FixedOrderGen/src/PhaseSpacePoint.cc b/FixedOrderGen/src/PhaseSpacePoint.cc
	index ad5efe9..64ce55a 100644
	--- a/FixedOrderGen/src/PhaseSpacePoint.cc
	+++ b/FixedOrderGen/src/PhaseSpacePoint.cc
	@@ -1,695 +1,695 @@
	/**
	* \authors The HEJ collaboration (see AUTHORS for details)
	* \date 2019
	* \copyright GPLv2 or later
	*/
	#include "PhaseSpacePoint.hh"

	#include <algorithm>

	#include "CLHEP/Vector/LorentzVector.h"

	#include "HEJ/Constants.hh"
	#include "HEJ/EWConstants.hh"
	#include "HEJ/exceptions.hh"
	#include "HEJ/kinematics.hh"
	#include "HEJ/Particle.hh"
	#include "HEJ/utility.hh"

	#include "Process.hh"
	#include "Subleading.hh"

	using namespace HEJ;

	namespace HEJFOG{

	namespace {
	static_assert(
	std::numeric_limits<double>::has_quiet_NaN,
	"no quiet NaN for double"
	);
	constexpr double NaN = std::numeric_limits<double>::quiet_NaN();
	} // namespace anonymous

	HEJ::Event::EventData to_EventData(PhaseSpacePoint psp){
	//! @TODO Same function already in HEJ
	HEJ::Event::EventData result;
	result.incoming = std::move(psp).incoming_;
	assert(result.incoming.size() == 2);
	result.outgoing = std::move(psp).outgoing_;
	// technically Event::EventData doesn't have to be sorted,
	// but PhaseSpacePoint should be anyway
	assert(
	std::is_sorted(
	begin(result.outgoing), end(result.outgoing),
	HEJ::rapidity_less{}
	)
	);
	assert(result.outgoing.size() >= 2);
	result.decays = std::move(psp).decays_;
	result.parameters.central = {NaN, NaN, psp.weight()};
	return result;
	}

	namespace{
	bool can_swap_to_uno(
	HEJ::Particle const & p1, HEJ::Particle const & p2
	){
	return is_parton(p1)
	&& p1.type != pid::gluon
	&& p2.type == pid::gluon;
	}

	size_t count_gluons(std::vector<Particle>::const_iterator first,
	std::vector<Particle>::const_iterator last){
	return std::count_if(first, last, [](Particle const & p)
	{return p.type == pid::gluon;});
	}

	/** assumes FKL configurations between first and last,
	* else there can be a quark in a non-extreme position
	* e.g. uno configuration gqg would pass
	*/
	bool can_change_to_qqx(
	std::vector<Particle>::const_iterator first,
	std::vector<Particle>::const_iterator last){
	return 1 < count_gluons(first,last);
	}
	bool is_AWZ_proccess(Process const & proc){
	return proc.boson && is_AWZ_boson(*proc.boson);
	}

	bool is_up_type(Particle const & part){
	return HEJ::is_anyquark(part) && !(abs(part.type)%2);
	}
	bool is_down_type(Particle const & part){
	return HEJ::is_anyquark(part) && abs(part.type)%2;
	}
	bool can_couple_to_W(Particle const & part, pid::ParticleID const W_id){
	const int W_charge = W_id>0?1:-1;
	return abs(part.type)<5
	&& ( (W_charge*part.type > 0 && is_up_type(part))
	\|\| (W_charge*part.type < 0 && is_down_type(part)) );
	}
	}

	void PhaseSpacePoint::maybe_turn_to_subl(
	double chance,
	unsigned int const channels,
	Process const & proc,
	HEJ::RNG & ran
	){
	if(proc.njets <= 2) return;
	assert(outgoing_.size() >= 2);

	// decide what kind of subleading process is allowed
	bool allow_uno = false;
	bool allow_strange = true;
	const size_t nout = outgoing_.size();
	const bool can_be_uno_backward = (channels&Subleading::uno)
	&& can_swap_to_uno(outgoing_[0], outgoing_[1]);
	const bool can_be_uno_forward = (channels&Subleading::uno)
	&& can_swap_to_uno(outgoing_[nout-1], outgoing_[nout-2]);
	allow_uno = can_be_uno_backward \|\| can_be_uno_forward;

	bool allow_qqx = (channels&Subleading::qqx)
	&& can_change_to_qqx(outgoing_.cbegin(), outgoing_.cend());
	if(is_AWZ_proccess(proc)) {
	if(std::none_of(outgoing_.cbegin(), outgoing_.cend(),
	[&proc](Particle const & p){ return can_couple_to_W(p, *proc.boson);})) {
	// enforce qqx if A/W/Z can't couple somewhere else
	assert(allow_qqx);
	allow_uno = false;
	chance = 1.;
	// strange not allowed for W
	if(abs(*proc.boson)== pid::Wp) allow_strange = false;
	}
	}

	if(!allow_uno && !allow_qqx) return;
	if(ran.flat() < chance){
	weight_ /= chance;
	if(allow_uno && !allow_qqx){
	turn_to_uno(can_be_uno_backward, can_be_uno_forward, ran);
	} else if (!allow_uno && allow_qqx) {
	turn_to_qqx(allow_strange, ran);
	} else {
	assert( allow_uno && allow_qqx);
	if(ran.flat() < 0.5) turn_to_uno(can_be_uno_backward, can_be_uno_forward, ran);
	else turn_to_qqx(allow_strange, ran);
	weight_ *= 2.;
	}
	} else weight_ /= 1 - chance;

	}

	void PhaseSpacePoint::turn_to_uno(
	const bool can_be_uno_backward, const bool can_be_uno_forward,
	HEJ::RNG & ran
	){
	if(!can_be_uno_backward && !can_be_uno_forward) return;
	const size_t nout = outgoing_.size();
	if(can_be_uno_backward && can_be_uno_forward){
	if(ran.flat() < 0.5){
	std::swap(outgoing_[0].type, outgoing_[1].type);
	} else {
	std::swap(outgoing_[nout-1].type, outgoing_[nout-2].type);
	}
	weight_ *= 2.;
	} else if(can_be_uno_backward){
	std::swap(outgoing_[0].type, outgoing_[1].type);
	} else {
	assert(can_be_uno_forward);
	std::swap(outgoing_[nout-1].type, outgoing_[nout-2].type);
	}
	}

	void PhaseSpacePoint::turn_to_qqx(const bool allow_strange, HEJ::RNG & ran){
	/// find first and last gluon in FKL chain
	auto first = std::find_if(outgoing_.begin(), outgoing_.end(),
	[](Particle const & p){return p.type == pid::gluon;});
	std::vector<Particle*> FKL_gluons;
	for(auto p = first; p!=outgoing_.end(); ++p){
	if(p->type == pid::gluon) FKL_gluons.push_back(&*p);
	else if(is_anyquark(*p)) break;
	}
	const size_t ng = FKL_gluons.size();
	if(ng < 2)
	throw std::logic_error("not enough gluons to create qqx");
	// select flavour of quark
	const double r1 = 2.*ran.flat()-1.;
	const double max_flavour = allow_strange?n_f:n_f-1;
	weight_ = max_flavour2;
	int flavour = pid::down + std::floor(std::abs(r1)*max_flavour);
	flavour*=r1<0.?-1:1;
	// select gluon for switch
	const size_t idx = floor((ng-1) * ran.flat());
	weight_ *= (ng-1);
	FKL_gluons[idx]->type = ParticleID(flavour);
	FKL_gluons[idx+1]->type = ParticleID(-flavour);
	}

	template<class ParticleMomenta>
	fastjet::PseudoJet PhaseSpacePoint::gen_last_momentum(
	ParticleMomenta const & other_momenta,
	const double mass_square, const double y
	) const {
	std::array<double,2> pt{0.,0.};
	for (auto const & p: other_momenta) {
	pt[0]-= p.px();
	pt[1]-= p.py();
	}

	const double mperp = sqrt(pt[0]pt[0]+pt[1]pt[1]+mass_square);
	const double pz=mperp*sinh(y);
	const double E=mperp*cosh(y);

	return {pt[0], pt[1], pz, E};
	}

	namespace {
	//! adds a particle to target (in correct rapidity ordering)
	//! @returns positon of insertion
	auto insert_particle(std::vector<HEJ::Particle> & target,
	HEJ::Particle && particle
	){
	const auto pos = std::upper_bound(
	begin(target),end(target),particle,rapidity_less{}
	);
	target.insert(pos, std::move(particle));
	return pos;
	}
	}

	PhaseSpacePoint::PhaseSpacePoint(
	Process const & proc,
	JetParameters const & jet_param,
	HEJ::PDF & pdf, double E_beam,
	double const subl_chance,
	unsigned int const subl_channels,
	ParticlesDecayMap const & particle_decays,
	HEJ::EWConstants const & ew_parameters,
	HEJ::RNG & ran
	)
	{
	assert(proc.njets >= 2);
	status_ = good;
	weight_ = 1;

	const int nout = proc.njets + (proc.boson?1:0) + proc.boson_decay.size();
	outgoing_.reserve(nout);

	// generate parton momenta
	const bool is_pure_jets = (nout == proc.njets);
	auto partons = gen_LO_partons(
	proc.njets, is_pure_jets, jet_param, E_beam, ran
	);
	// pre fill flavour with gluons
	for(auto&& p_out: partons) {
	outgoing_.emplace_back(Particle{pid::gluon, std::move(p_out), {}});
	}
	if(status_ != good) return;

	if(proc.boson){ // decay boson
	const auto & boson_prop = ew_parameters.prop(*proc.boson) ;
	auto boson{ gen_boson(*proc.boson, boson_prop.mass, boson_prop.width, ran) };
	const auto pos{insert_particle(outgoing_, std::move(boson))};
	const size_t boson_idx = std::distance(begin(outgoing_), pos);
	const auto & boson_decay = particle_decays.find(*proc.boson);
	if( !proc.boson_decay.empty() ){ // decay given in proc
	decays_.emplace(
	boson_idx,
	decay_boson(outgoing_[boson_idx], proc.boson_decay, ran)
	);
	} else if( boson_decay != particle_decays.end()
	&& !boson_decay->second.empty() ){ // decay given explicitly
	decays_.emplace(
	boson_idx,
	decay_boson(outgoing_[boson_idx], boson_decay->second, ran)
	);
	}
	}
	// normalisation of momentum-conserving delta function
	weight_ = pow(2M_PI, 4);

	/** @TODO
	* uf (jet_param.min_pt) doesn't correspond to our final scale choice.
	* The HEJ scale generators currently expect a full event as input,
	* so fixing this is not completely trivial
	*/
	reconstruct_incoming(proc, subl_channels, pdf, E_beam, jet_param.min_pt, ran);
	if(status_ != good) return;
	// set outgoing states
	most_backward_FKL(outgoing_).type = incoming_[0].type;
	most_forward_FKL(outgoing_).type = incoming_[1].type;

	maybe_turn_to_subl(subl_chance, subl_channels, proc, ran);

	if(proc.boson) couple_boson(*proc.boson, ran);
	}

	double PhaseSpacePoint::gen_hard_pt(
	int np , double ptmin, double ptmax, double y,
	HEJ::RNG & ran
	) {
	// heuristic parameters for pt sampling
	const double ptpar = ptmin + np/5.;
	const double arg_small_y = atan((ptmax - ptmin)/ptpar);
	const double y_cut = 3.;

	const double r1 = ran.flat();
	if(y < y_cut){
	const double pt = ptmin + ptpartan(r1arg_small_y);
	const double temp = cos(r1*arg_small_y);
	weight_ = ptptpararg_small_y/(temptemp);
	return pt;
	}

	const double ptpar2 = ptpar/(1 + 5*(y-y_cut));
	const double temp = 1. - std::exp((ptmin-ptmax)/ptpar2);
	const double pt = ptmin - ptpar2std::log(1-r1temp);
	weight_ = ptptpar2temp/(1-r1temp);
	return pt;
	}

	double PhaseSpacePoint::gen_soft_pt(int np, double max_pt, HEJ::RNG & ran) {
	constexpr double ptpar = 4.;

	const double r = ran.flat();
	const double pt = max_pt + ptpar/np*std::log(r);
	weight_ = ptptpar/(np*r);
	return pt;
	}

	double PhaseSpacePoint::gen_parton_pt(
	int count, JetParameters const & jet_param, double max_pt, double y,
	HEJ::RNG & ran
	) {
	constexpr double p_small_pt = 0.02;

	if(! jet_param.peak_pt) {
	return gen_hard_pt(count, jet_param.min_pt, max_pt, y, ran);
	}
	const double r = ran.flat();
	if(r > p_small_pt) {
	weight_ /= 1. - p_small_pt;
	return gen_hard_pt(count, *jet_param.peak_pt, max_pt, y, ran);
	}
	weight_ /= p_small_pt;
	const double pt = gen_soft_pt(count, *jet_param.peak_pt, ran);
	if(pt < jet_param.min_pt) {
	weight_=0.0;
	status_ = not_enough_jets;
	return jet_param.min_pt;
	}
	return pt;
	}

	std::vector<fastjet::PseudoJet> PhaseSpacePoint::gen_LO_partons(
	int np, bool is_pure_jets,
	JetParameters const & jet_param,
	double max_pt,
	HEJ::RNG & ran
	){
	if (np<2) throw std::invalid_argument{"Not enough partons in gen_LO_partons"};

	weight_ /= pow(16.*pow(M_PI,3),np);
	weight_ /= std::tgamma(np+1); //remove rapidity ordering
	std::vector<fastjet::PseudoJet> partons;
	partons.reserve(np);
	for(int i = 0; i < np; ++i){
	const double y = -jet_param.max_y + 2jet_param.max_yran.flat();
	weight_ = 2jet_param.max_y;

	const bool is_last_parton = i+1 == np;
	if(is_pure_jets && is_last_parton) {
	constexpr double parton_mass_sq = 0.;
	partons.emplace_back(gen_last_momentum(partons, parton_mass_sq, y));
	break;
	}

	const double phi = 2M_PIran.flat();
	weight_ = 2.0M_PI;

	const double pt = gen_parton_pt(np, jet_param, max_pt, y, ran);
	if(weight_ == 0.0) return {};

	partons.emplace_back(fastjet::PtYPhiM(pt, y, phi));
	assert(jet_param.min_pt <= partons[i].pt());
	assert(partons[i].pt() <= max_pt+1e-5);
	}
	// Need to check that at LO, the number of jets = number of partons;
	fastjet::ClusterSequence cs(partons, jet_param.def);
	auto cluster_jets=cs.inclusive_jets(jet_param.min_pt);
	if (cluster_jets.size()!=unsigned(np)){
	weight_=0.0;
	status_ = not_enough_jets;
	return {};
	}

	std::sort(begin(partons), end(partons), rapidity_less{});

	return partons;
	}

	Particle PhaseSpacePoint::gen_boson(
	HEJ::ParticleID bosonid, double mass, double width,
	HEJ::RNG & ran
	){
	// Usual phase space measure
	weight_ /= 16.*pow(M_PI, 3);

	// Generate a y Gaussian distributed around 0
	/// @TODO check magic numbers for different boson Higgs
	/// @TODO better sampling for W
	const double stddev_y = 1.6;
	const double y = random_normal(stddev_y, ran);
	const double r1 = ran.flat();
	const double s_boson = mass*(
	mass + widthtan(M_PI/2.r1 + (r1-1.)*atan(mass/width))
	);
	// off-shell s_boson sampling, compensates for Breit-Wigner
	/// @TODO use a flag instead
	if(abs(bosonid) == pid::Wp){
	weight_/=M_PIM_PI8.;
	weight_= masswidth( M_PI+2.atan(mass/width) )
	/ ( 1. + cos( M_PIr1 + 2.(r1-1.)*atan(mass/width) ) );
	}

	auto p = gen_last_momentum(outgoing_, s_boson, y);

	return Particle{bosonid, std::move(p), {}};
	}

	Particle const & PhaseSpacePoint::most_backward_FKL(
	std::vector<Particle> const & partons
	) const{
	if(!HEJ::is_parton(partons[0])) return partons[1];
	return partons[0];
	}

	Particle const & PhaseSpacePoint::most_forward_FKL(
	std::vector<Particle> const & partons
	) const{
	const size_t last_idx = partons.size() - 1;
	if(!HEJ::is_parton(partons[last_idx])) return partons[last_idx-1];
	return partons[last_idx];
	}

	Particle & PhaseSpacePoint::most_backward_FKL(
	std::vector<Particle> & partons
	) const{
	if(!HEJ::is_parton(partons[0])) return partons[1];
	return partons[0];
	}

	Particle & PhaseSpacePoint::most_forward_FKL(
	std::vector<Particle> & partons
	) const{
	const size_t last_idx = partons.size() - 1;
	if(!HEJ::is_parton(partons[last_idx])) return partons[last_idx-1];
	return partons[last_idx];
	}

	namespace {
	/// partons are ordered: even = anti, 0 = gluon
	ParticleID index_to_pid(size_t i){
	if(!i) return pid::gluon;
	return static_cast<ParticleID>( i%2 ? (i+1)/2 : -i/2 );
	}

	/// partons are ordered: even = anti, 0 = gluon
	size_t pid_to_index(ParticleID id){
	if(id==pid::gluon) return 0;
	return id>0 ? id2-1 : abs(id)2;
	}

	std::bitset<11> init_allowed(ParticleID const id){
	if(abs(id) == pid::proton)
	return ~0;
	std::bitset<11> out{0};
	if(is_parton(id))
	out[pid_to_index(id)] = 1;
	return out;
	}

	/// decides which "index" (see index_to_pid) are allowed for process
	std::bitset<11> allowed_quarks(ParticleID const boson){
	std::bitset<11> allowed = ~0;
	if(abs(boson) == pid::Wp){
	// special case W:
	// Wp: anti-down or up-type quark, no b/t
	// Wm: down or anti-up-type quark, no b/t
	allowed = boson>0? 0b00011001101
	:0b00100110011;
	}
	return allowed;
	}
	}

	/**
	* checks which partons are allowed as initial state:
	* 1. only allow what is given in the Runcard (p -> all)
	* 2. A/W/Z require something to couple to
	* a) no qqx => no incoming gluon
	* b) 2j => no incoming gluon
	* c) 3j => can couple OR is gluon => 2 gluons become qqx later
	*/
	std::array<std::bitset<11>,2> PhaseSpacePoint::filter_partons(
	Process const & proc, unsigned int const subl_channels, HEJ::RNG & ran
	){
	std::array<std::bitset<11>,2> allowed_partons{
	init_allowed(proc.incoming[0]),
	init_allowed(proc.incoming[1])
	};
	bool const allow_qqx = subl_channels&Subleading::qqx;
	// special case A/W/Z
	if(is_AWZ_proccess(proc) && ((proc.njets < 4) \|\| !allow_qqx)){
	// all possible incoming states
	auto allowed(allowed_quarks(*proc.boson));
	if(proc.njets == 2 \|\| !allow_qqx) allowed[0]=0;

	// possible states per leg
	std::array<std::bitset<11>,2> const maybe_partons{
	allowed_partons[0]&allowed, allowed_partons[1]&allowed};

	if(maybe_partons[0].any() && maybe_partons[1].any()){
	// two options to get allowed initial state => choose one at random
	const size_t idx = ran.flat() < 0.5;
	allowed_partons[idx] = maybe_partons[idx];
	// else choose the possible
	} else if(maybe_partons[0].any()) {
	allowed_partons[0] = maybe_partons[0];
	} else if(maybe_partons[1].any()) {
	allowed_partons[1] = maybe_partons[1];
	} else{
	throw std::invalid_argument{"Incoming state not allowed."};
	}
	}
	return allowed_partons;
	}

	void PhaseSpacePoint::reconstruct_incoming(
	Process const & proc, unsigned int const subl_channels,
	HEJ::PDF & pdf, double E_beam,
	double uf,
	HEJ::RNG & ran
	){
	std::tie(incoming_[0].p, incoming_[1].p) = incoming_momenta(outgoing_);
	// calculate xa, xb
	const double sqrts=2*E_beam;
	- const double xa=(incoming_[0].p.e()-incoming_[0].p.pz())/sqrts;
	- const double xb=(incoming_[1].p.e()+incoming_[1].p.pz())/sqrts;
	+ const double xa=(incoming_[0].E()-incoming_[0].pz())/sqrts;
	+ const double xb=(incoming_[1].E()+incoming_[1].pz())/sqrts;
	// abort if phase space point is outside of collider energy reach
	if (xa>1. \|\| xb>1.){
	weight_=0;
	status_ = too_much_energy;
	return;
	}
	auto const & ids = proc.incoming;
	std::array<std::bitset<11>,2> allowed_partons(
	filter_partons(proc, subl_channels, ran));
	for(size_t i = 0; i < 2; ++i){
	if(ids[i] == pid::proton \|\| ids[i] == pid::p_bar){
	// pick ids according to pdfs
	incoming_[i].type =
	generate_incoming_id(i, i?xb:xa, uf, pdf, allowed_partons[i], ran);
	} else {
	assert(allowed_partons[i][pid_to_index(ids[i])]);
	incoming_[i].type = ids[i];
	}
	}
	assert(momentum_conserved(1e-7));
	}

	HEJ::ParticleID PhaseSpacePoint::generate_incoming_id(
	size_t const beam_idx, double const x, double const uf,
	HEJ::PDF & pdf, std::bitset<11> allowed_partons, HEJ::RNG & ran
	){
	std::array<double,11> pdf_wt;
	pdf_wt[0] = allowed_partons[0]?fabs(pdf.pdfpt(beam_idx,x,uf,pid::gluon)):0.;
	double pdftot = pdf_wt[0];
	for(size_t i = 1; i < pdf_wt.size(); ++i){
	pdf_wt[i] = allowed_partons[i]?4./9.*fabs(pdf.pdfpt(beam_idx,x,uf,index_to_pid(i))):0;
	pdftot += pdf_wt[i];
	}
	const double r1 = pdftot * ran.flat();
	double sum = 0;
	for(size_t i=0; i < pdf_wt.size(); ++i){
	if (r1 < (sum+=pdf_wt[i])){
	weight_*= pdftot/pdf_wt[i];
	return index_to_pid(i);
	}
	}
	std::cerr << "Error in choosing incoming parton: "<<x<<" "<<uf<<" "
	<<sum<<" "<<pdftot<<" "<<r1<<std::endl;
	throw std::logic_error{"Failed to choose parton flavour"};
	}

	void PhaseSpacePoint::couple_boson(
	HEJ::ParticleID const boson, HEJ::RNG & ran
	){
	if(abs(boson) != pid::Wp) return; // only matters for W
	/// @TODO this could be use to sanity check gamma and Z

	// find all possible quarks
	std::vector<Particle*> allowed_parts;
	for(auto & part: outgoing_){
	// Wp -> up OR anti-down, Wm -> anti-up OR down, no bottom
	if ( can_couple_to_W(part, boson) )
	allowed_parts.push_back(&part);
	}
	if(allowed_parts.size() == 0){
	throw std::logic_error{"Found no parton for coupling with boson"};
	}

	// select one and flip it
	size_t idx = 0;
	if(allowed_parts.size() > 1){
	/// @TODO more efficient sampling
	/// old code: probability[i] = exp(parton[i].y - W.y)
	idx = floor(ran.flat()*allowed_parts.size());
	weight_ *= allowed_parts.size();
	}
	const int W_charge = boson>0?1:-1;
	allowed_parts[idx]->type =
	static_cast<ParticleID>( allowed_parts[idx]->type - W_charge );
	}

	double PhaseSpacePoint::random_normal(
	double stddev,
	HEJ::RNG & ran
	){
	const double r1 = ran.flat();
	const double r2 = ran.flat();
	const double lninvr1 = -log(r1);
	const double result = stddevsqrt(2.lninvr1)cos(2.M_PI*r2);
	weight_ = exp(resultresult/(2stddevstddev))sqrt(2.M_PI)*stddev;
	return result;
	}

	bool PhaseSpacePoint::momentum_conserved(double ep) const{
	fastjet::PseudoJet diff;
	for(auto const & in: incoming()) diff += in.p;
	for(auto const & out: outgoing()) diff -= out.p;
	return nearby_ep(diff, fastjet::PseudoJet{}, ep);
	}

	Decay PhaseSpacePoint::select_decay_channel(
	std::vector<Decay> const & decays,
	HEJ::RNG & ran
	){
	double br_total = 0.;
	for(auto const & decay: decays) br_total += decay.branching_ratio;
	// adjust weight
	// this is given by (channel branching ratio)/(chance to pick channel)
	// where (chance to pick channel) =
	// (channel branching ratio)/(total branching ratio)
	weight_ *= br_total;
	if(decays.size()==1) return decays.front();
	const double r1 = br_total*ran.flat();
	double br_sum = 0.;
	for(auto const & decay: decays){
	br_sum += decay.branching_ratio;
	if(r1 < br_sum) return decay;
	}
	throw std::logic_error{"unreachable"};
	}

	std::vector<Particle> PhaseSpacePoint::decay_boson(
	HEJ::Particle const & parent,
	std::vector<Decay> const & decays,
	HEJ::RNG & ran
	){
	const auto channel = select_decay_channel(decays, ran);
	return decay_boson(parent, channel.products, ran);
	}

	std::vector<Particle> PhaseSpacePoint::decay_boson(
	HEJ::Particle const & parent,
	std::vector<HEJ::ParticleID> const & decays,
	HEJ::RNG & ran
	){
	if(decays.size() != 2){
	throw HEJ::not_implemented{
	"only decays into two particles are implemented"
	};
	}
	std::vector<Particle> decay_products(decays.size());
	for(size_t i = 0; i < decays.size(); ++i){
	decay_products[i].type = decays[i];
	}
	// choose polar and azimuth angle in parent rest frame
	const double E = parent.m()/2;
	const double theta = 2.M_PIran.flat();
	const double cos_phi = 2.*ran.flat()-1.;
	const double sin_phi = sqrt(1. - cos_phi*cos_phi); // Know 0 < phi < pi
	const double px = Ecos(theta)sin_phi;
	const double py = Esin(theta)sin_phi;
	const double pz = E*cos_phi;
	decay_products[0].p.reset(px, py, pz, E);
	decay_products[1].p.reset(-px, -py, -pz, E);
	for(auto & particle: decay_products) particle.p.boost(parent.p);
	return decay_products;
	}
	}
	diff --git a/src/PhaseSpacePoint.cc b/src/PhaseSpacePoint.cc
	index 6b47ca1..d3b8dbc 100644
	--- a/src/PhaseSpacePoint.cc
	+++ b/src/PhaseSpacePoint.cc
	@@ -1,838 +1,840 @@
	/**
	* \authors The HEJ collaboration (see AUTHORS for details)
	* \date 2019
	* \copyright GPLv2 or later
	*/
	#include "HEJ/PhaseSpacePoint.hh"

	#include <algorithm>
	#include <assert.h>
	#include <numeric>
	#include <random>

	#include "fastjet/ClusterSequence.hh"

	#include "HEJ/Constants.hh"
	#include "HEJ/Event.hh"
	#include "HEJ/JetSplitter.hh"
	#include "HEJ/kinematics.hh"
	#include "HEJ/resummation_jet.hh"
	#include "HEJ/utility.hh"
	#include "HEJ/PDG_codes.hh"
	#include "HEJ/event_types.hh"

	namespace HEJ{
	namespace {
	constexpr int max_jet_user_idx = PhaseSpacePoint::ng_max;

	bool is_nonjet_parton(fastjet::PseudoJet const & parton){
	assert(parton.user_index() != -1);
	return parton.user_index() > max_jet_user_idx;
	}

	bool is_jet_parton(fastjet::PseudoJet const & parton){
	assert(parton.user_index() != -1);
	return parton.user_index() <= max_jet_user_idx;
	}

	// user indices for partons with extremal rapidity
	constexpr int qqxmid1_uid = -9;
	constexpr int qqxmid2_uid = -8;
	constexpr int qqxb_uid = -7;
	constexpr int qqxf_uid = -6;
	constexpr int unob_uid = -5;
	constexpr int unof_uid = -4;
	constexpr int backward_FKL_uid = -3;
	constexpr int forward_FKL_uid = -2;

	double estimate_ng_mean(std::vector<fastjet::PseudoJet> const & Born_jets){
	const double delta_y =
	Born_jets.back().rapidity() - Born_jets.front().rapidity();
	assert(delta_y > 0);
	// Formula derived from fit in arXiv:1805.04446 (see Fig. 2)
	return 0.975052*delta_y;
	}

	static_assert(
	std::numeric_limits<double>::has_quiet_NaN,
	"no quiet NaN for double"
	);
	constexpr double NaN = std::numeric_limits<double>::quiet_NaN();

	} // namespace anonymous

	Event::EventData to_EventData(PhaseSpacePoint psp){
	Event::EventData result;
	result.incoming = std::move(psp).incoming_;
	assert(result.incoming.size() == 2);
	result.outgoing = std::move(psp).outgoing_;
	// technically Event::EventData doesn't have to be sorted,
	// but PhaseSpacePoint should be anyway
	assert(
	std::is_sorted(
	begin(result.outgoing), end(result.outgoing),
	HEJ::rapidity_less{}
	)
	);
	assert(result.outgoing.size() >= 2);
	result.decays = std::move(psp).decays_;
	result.parameters.central = {NaN, NaN, psp.weight()};
	return result;
	}

	std::vector<fastjet::PseudoJet> PhaseSpacePoint::cluster_jets(
	std::vector<fastjet::PseudoJet> const & partons
	) const{
	fastjet::ClusterSequence cs(partons, param_.jet_param.def);
	return sorted_by_rapidity(cs.inclusive_jets(param_.jet_param.min_pt));
	}

	bool PhaseSpacePoint::pass_resummation_cuts(
	std::vector<fastjet::PseudoJet> const & jets
	) const{
	return cluster_jets(jets).size() == jets.size();
	}

	int PhaseSpacePoint::sample_ng(
	std::vector<fastjet::PseudoJet> const & Born_jets, RNG & ran
	){
	const double ng_mean = estimate_ng_mean(Born_jets);
	std::poisson_distribution<int> dist(ng_mean);
	const int ng = dist(ran);
	assert(ng >= 0);
	assert(ng < ng_max);
	weight_ = std::tgamma(ng + 1)std::exp(ng_mean)*std::pow(ng_mean, -ng);
	return ng;
	}

	void PhaseSpacePoint::copy_AWZH_boson_from(Event const & event){
	auto const & from = event.outgoing();

	const auto AWZH_boson = std::find_if(
	begin(from), end(from),
	[](Particle const & p){ return is_AWZH_boson(p); }
	);
	if(AWZH_boson == end(from)) return;
	auto insertion_point = std::lower_bound(
	begin(outgoing_), end(outgoing_), *AWZH_boson, rapidity_less{}
	);
	outgoing_.insert(insertion_point, *AWZH_boson);

	// copy decay products
	const int idx = std::distance(begin(from), AWZH_boson);
	assert(idx >= 0);
	const auto decay_it = event.decays().find(idx);
	if(decay_it != end(event.decays())){
	const int new_idx = std::distance(begin(outgoing_), insertion_point);
	assert(new_idx >= 0);
	assert(outgoing_[new_idx].type == AWZH_boson->type);
	decays_.emplace(new_idx, decay_it->second);
	}

	assert(std::is_sorted(begin(outgoing_), end(outgoing_), rapidity_less{}));
	}

	namespace {

	auto get_first_anyquark_emission(Event const & ev) {
	// find born quarks (ignore extremal partons)
	auto const firstquark = std::find_if(
	std::next(ev.begin_partons()), std::prev(ev.end_partons(), 2),
	[](Particle const & s){ return (is_anyquark(s)); }
	);
	// assert that it is a q-q_bar pair.
	assert(std::distance(firstquark, ev.end_partons()) != 2);
	assert(
	( is_quark(firstquark) && is_antiquark(std::next(firstquark)) )
	\|\| ( is_antiquark(firstquark) && is_quark(std::next(firstquark)) )
	);
	return firstquark;
	}

	//! returns index of most backward q-qbar jet
	template<class Iterator>
	int get_back_quark_jet(Event const & ev, Iterator firstquark){
	// find jets at FO corresponding to the quarks
	// technically this isn't necessary for LO
	std::vector<int> const born_indices{ ev.particle_jet_indices() };
	const auto firstquark_idx = std::distance(ev.begin_partons(), firstquark);
	int const firstjet_idx = born_indices[firstquark_idx];
	assert(firstjet_idx>0);
	assert( born_indices[firstquark_idx+1] == firstjet_idx+1 );

	return firstjet_idx;
	}

	//! returns index of most backward q-qbar jet
	int getBackQuarkJet(Event const & ev){
	const auto firstquark = get_first_anyquark_emission(ev);
	return get_back_quark_jet(ev, firstquark);
	}

	template<class ConstIterator, class Iterator>
	void label_extremal_qqx(
	ConstIterator born_begin, ConstIterator born_end,
	Iterator first_out
	){
	// find born quarks
	const auto firstquark = std::find_if(
	born_begin, born_end-1,
	[](Particle const & s){ return (is_anyquark(s)); }
	);
	assert(firstquark != born_end-1);
	const auto secondquark = std::find_if(
	firstquark+1, born_end,
	[](Particle const & s){ return (is_anyquark(s)); }
	);
	assert(secondquark != born_end);
	assert( ( is_quark(firstquark) && is_antiquark(secondquark) )
	\|\| ( is_antiquark(firstquark) && is_quark(secondquark) ));
	assert(first_out->type == ParticleID::gluon);
	assert((first_out+1)->type == ParticleID::gluon);

	// copy type from born
	first_out->type = firstquark->type;
	(first_out+1)->type = secondquark->type;
	}
	}

	void PhaseSpacePoint::label_qqx(Event const & event){
	assert(std::is_sorted(begin(outgoing_), end(outgoing_), rapidity_less{}));
	assert(filter_partons(outgoing_).size() == outgoing_.size());
	if(qqxb_){
	label_extremal_qqx( event.outgoing().cbegin(), event.outgoing().cend(),
	outgoing_.begin()
	);
	return;
	}
	if(qqxf_){ // same as qqxb with reversed order
	label_extremal_qqx( event.outgoing().crbegin(), event.outgoing().crend(),
	outgoing_.rbegin()
	);
	return;
	}
	// central qqx
	const auto firstquark = get_first_anyquark_emission(event);

	// find jets at FO corresponding to the quarks
	// technically this isn't necessary for LO
	const auto firstjet_idx = get_back_quark_jet(event, firstquark);

	// find corresponding jets after resummation
	fastjet::ClusterSequence cs{to_PseudoJet(outgoing_), param_.jet_param.def};
	auto const jets = fastjet::sorted_by_rapidity(
	cs.inclusive_jets( param_.jet_param.min_pt ));
	std::vector<int> const resum_indices{ cs.particle_jet_indices({jets}) };

	// assert that jets didn't move
	assert(nearby_ep( ( event.jets().cbegin()+firstjet_idx )->rapidity(),
	jets[ firstjet_idx ].rapidity(), 1e-2) );
	assert(nearby_ep( ( event.jets().cbegin()+firstjet_idx+1 )->rapidity(),
	jets[ firstjet_idx+1 ].rapidity(), 1e-2) );

	// find last partons in first (central) jet
	size_t idx_out = 0;
	for(size_t i=resum_indices.size()-2; i>0; --i)
	if(resum_indices[i] == firstjet_idx){
	idx_out = i;
	break;
	}
	assert(idx_out != 0);

	// check that there is sufficient pt in jets from the quarks
	const double minpartonjetpt = 1. - param_.max_ext_soft_pt_fraction;
	if (outgoing_[idx_out].p.pt()<minpartonjetpt*( event.jets().cbegin()+firstjet_idx )->pt()){
	weight_=0.;
	status_ = StatusCode::wrong_jets;
	return;
	}

	if (outgoing_[idx_out+1].p.pt()<minpartonjetpt*( event.jets().cbegin()+firstjet_idx+1 )->pt()){
	weight_=0.;
	status_ = StatusCode::wrong_jets;
	return;
	}
	// check that no additional emission between jets
	// such configurations are possible if we have an gluon gets generated
	// inside the rapidities of the qqx chain, but clusted to a
	// differnet/outside jet. Changing this is non trivial
	if(resum_indices[idx_out+1] != resum_indices[idx_out]+1){
	weight_=0.;
	status_ = StatusCode::gluon_in_qqx;
	return;
	}
	outgoing_[idx_out].type = firstquark->type;
	outgoing_[idx_out+1].type = std::next(firstquark)->type;
	}

	void PhaseSpacePoint::label_quarks(Event const & ev){
	const auto WEmit = std::find_if(
	begin(ev.outgoing()), end(ev.outgoing()),
	[](Particle const & s){ return abs(s.type) == pid::Wp; }
	);

	if (WEmit != end(ev.outgoing())){
	if(!qqxb_) {
	const size_t backward_FKL_idx = unob_?1:0;
	const auto backward_FKL = std::next(ev.begin_partons(), backward_FKL_idx);
	outgoing_[backward_FKL_idx].type = backward_FKL->type;
	}
	if(!qqxf_) {
	const size_t forward_FKL_idx = unof_?1:0;
	const auto forward_FKL = std::prev(ev.end_partons(), 1+forward_FKL_idx);
	outgoing_.rbegin()[unof_].type = forward_FKL->type;
	}
	} else {
	most_backward_FKL(outgoing_).type = ev.incoming().front().type;
	most_forward_FKL(outgoing_).type = ev.incoming().back().type;
	}

	if(qqxmid_\|\|qqxb_\|\|qqxf_){
	label_qqx(ev);
	}
	}

	PhaseSpacePoint::PhaseSpacePoint(
	Event const & ev, PhaseSpacePointConfig conf, RNG & ran
	):
	unob_{ev.type() == event_type::unob},
	unof_{ev.type() == event_type::unof},
	qqxb_{ev.type() == event_type::qqxexb},
	qqxf_{ev.type() == event_type::qqxexf},
	qqxmid_{ev.type() == event_type::qqxmid},
	param_{std::move(conf)},
	status_{unspecified}
	{
	weight_ = 1;
	const auto & Born_jets = ev.jets();
	const int ng = sample_ng(Born_jets, ran);
	weight_ /= std::tgamma(ng + 1);
	const int ng_jets = sample_ng_jets(ng, Born_jets, ran);
	std::vector<fastjet::PseudoJet> out_partons = gen_non_jet(
	ng - ng_jets, CMINPT, param_.jet_param.min_pt, ran
	);

	int qqxbackjet(-1);
	if(qqxmid_){
	qqxbackjet = getBackQuarkJet(ev);
	}

	const auto qperp = std::accumulate(
	begin(out_partons), end(out_partons),
	fastjet::PseudoJet{}
	);
	const auto jets = reshuffle(Born_jets, qperp);
	if(weight_ == 0.) {
	status_ = failed_reshuffle;
	return;
	}
	if(! pass_resummation_cuts(jets)){
	status_ = failed_resummation_cuts;
	weight_ = 0.;
	return;
	}
	std::vector<fastjet::PseudoJet> jet_partons = split(
	jets, ng_jets, qqxbackjet, ran
	);
	if(weight_ == 0.) {
	status_ = StatusCode::failed_split;
	return;
	}
	if(qqxmid_){
	rescale_qqx_rapidities(
	out_partons, jets,
	most_backward_FKL(jet_partons).rapidity(),
	most_forward_FKL(jet_partons).rapidity(),
	qqxbackjet
	);
	}
	else{
	rescale_rapidities(
	out_partons,
	most_backward_FKL(jet_partons).rapidity(),
	most_forward_FKL(jet_partons).rapidity()
	);
	}
	if(! cluster_jets(out_partons).empty()){
	weight_ = 0.;
	status_ = StatusCode::empty_jets;
	return;
	}
	std::sort(begin(out_partons), end(out_partons), rapidity_less{});
	assert(
	std::is_sorted(begin(jet_partons), end(jet_partons), rapidity_less{})
	);
	const auto first_jet_parton = out_partons.insert(
	end(out_partons), begin(jet_partons), end(jet_partons)
	);
	std::inplace_merge(
	begin(out_partons), first_jet_parton, end(out_partons), rapidity_less{}
	);

	if(! jets_ok(Born_jets, out_partons)){
	weight_ = 0.;
	status_ = StatusCode::wrong_jets;
	return;
	}

	weight_ *= phase_space_normalisation(Born_jets.size(), out_partons.size());

	outgoing_.reserve(out_partons.size() + 1); // one slot for possible A, W, Z, H
	for(auto & p: out_partons){
	outgoing_.emplace_back(Particle{pid::gluon, std::move(p), {}});
	}
	assert(!outgoing_.empty());

	label_quarks(ev);
	if(weight_ == 0.) {
	//! @TODO optimise s.t. this is not possible
	// status is handled internally
	return;
	}

	copy_AWZH_boson_from(ev);

	reconstruct_incoming(ev.incoming());
	status_ = StatusCode::good;
	}

	std::vector<fastjet::PseudoJet> PhaseSpacePoint::gen_non_jet(
	int count, double ptmin, double ptmax, RNG & ran
	){
	// heuristic parameters for pt sampling
	const double ptpar = 1.3 + count/5.;
	const double temp1 = atan((ptmax - ptmin)/ptpar);

	std::vector<fastjet::PseudoJet> partons(count);
	for(size_t i = 0; i < static_cast<size_t>(count); ++i){
	const double r1 = ran.flat();
	const double pt = ptmin + ptpartan(r1temp1);
	const double temp2 = cos(r1*temp1);
	const double phi = 2M_PIran.flat();
	weight_ = 2.0M_PIptptpartemp1/(temp2temp2);
	// we don't know the allowed rapidity span yet,
	// set a random value to be rescaled later on
	const double y = ran.flat();
	partons[i].reset_PtYPhiM(pt, y, phi);
	// Set user index higher than any jet-parton index
	// in order to assert that these are not inside jets
	partons[i].set_user_index(i + 1 + ng_max);

	assert(ptmin-1e-5 <= partons[i].pt() && partons[i].pt() <= ptmax+1e-5);
	}
	assert(std::all_of(partons.cbegin(), partons.cend(), is_nonjet_parton));
	return sorted_by_rapidity(partons);
	}

	void PhaseSpacePoint::rescale_qqx_rapidities(
	std::vector<fastjet::PseudoJet> & out_partons,
	std::vector<fastjet::PseudoJet> const & jets,
	const double ymin1, const double ymax2,
	const int qqxbackjet
	){
	const double ymax1 = jets[qqxbackjet].rapidity();
	const double ymin2 = jets[qqxbackjet+1].rapidity();
	constexpr double ep = 1e-7;
	const double tot_y = ymax1 - ymin1 + ymax2 - ymin2;

	std::vector<std::reference_wrapper<fastjet::PseudoJet>> refpart(
	out_partons.begin(), out_partons.end());

	double ratio = (ymax1 - ymin1)/tot_y;

	const auto gap{ std::find_if(refpart.begin(), refpart.end(),
	[ratio](fastjet::PseudoJet p){
	return (p.rapidity()>=ratio);} ) };

	double ymin = ymin1;
	double ymax = ymax1;
	double dy = ymax - ymin - 2*ep;
	double offset = 0.;
	for(auto it_part=refpart.begin(); it_part<refpart.end(); ++it_part){
	if(it_part == gap){
	ymin = ymin2;
	ymax = ymax2;
	dy = ymax - ymin - 2*ep;
	offset = ratio;
	ratio = 1-ratio;
	}
	fastjet::PseudoJet & part = *it_part;
	assert(offset <= part.rapidity() && part.rapidity() < ratio+offset);
	const double y = ymin + ep + dy*((part.rapidity()-offset)/ratio);
	part.reset_momentum_PtYPhiM(part.pt(), y, part.phi());
	weight_ = tot_y-4.ep;
	assert(ymin <= part.rapidity() && part.rapidity() <= ymax);
	}
	assert(is_sorted(begin(out_partons), end(out_partons), rapidity_less{}));
	}

	void PhaseSpacePoint::rescale_rapidities(
	std::vector<fastjet::PseudoJet> & partons,
	double ymin, double ymax
	){
	constexpr double ep = 1e-7;
	for(auto & parton: partons){
	assert(0 <= parton.rapidity() && parton.rapidity() <= 1);
	const double dy = ymax - ymin - 2*ep;
	const double y = ymin + ep + dy*parton.rapidity();
	parton.reset_momentum_PtYPhiM(parton.pt(), y, parton.phi());
	weight_ *= dy;
	assert(ymin <= parton.rapidity() && parton.rapidity() <= ymax);
	}
	}

	namespace {
	template<typename T, typename... Rest>
	auto min(T const & a, T const & b, Rest&&... r) {
	using std::min;
	return min(a, min(b, std::forward<Rest>(r)...));
	}
	}

	double PhaseSpacePoint::probability_in_jet(
	std::vector<fastjet::PseudoJet> const & Born_jets
	) const{
	assert(std::is_sorted(begin(Born_jets), end(Born_jets), rapidity_less{}));
	assert(Born_jets.size() >= 2);

	const double dy =
	Born_jets.back().rapidity() - Born_jets.front().rapidity();
	const double R = param_.jet_param.def.R();
	const int njets = Born_jets.size();
	const double p_J_y_large = (njets-1)RR/(2.*dy);
	const double p_J_y0 = njets*R/M_PI;
	return min(p_J_y_large, p_J_y0, 1.);
	}

	int PhaseSpacePoint::sample_ng_jets(
	int ng, std::vector<fastjet::PseudoJet> const & Born_jets, RNG & ran
	){
	const double p_J = probability_in_jet(Born_jets);
	std::binomial_distribution<> bin_dist(ng, p_J);
	const int ng_J = bin_dist(ran);
	weight_ = std::pow(p_J, -ng_J)std::pow(1 - p_J, ng_J - ng);
	return ng_J;
	}

	std::vector<fastjet::PseudoJet> PhaseSpacePoint::reshuffle(
	std::vector<fastjet::PseudoJet> const & Born_jets,
	fastjet::PseudoJet const & q
	){
	if(q == fastjet::PseudoJet{0, 0, 0, 0}) return Born_jets;
	const auto jets = resummation_jet_momenta(Born_jets, q);
	if(jets.empty()){
	weight_ = 0;
	return {};
	}

	// additional Jacobian to ensure Born integration over delta gives 1
	weight_ *= resummation_jet_weight(Born_jets, q);
	return jets;
	}

	std::vector<int> PhaseSpacePoint::distribute_jet_partons(
	int ng_jets, std::vector<fastjet::PseudoJet> const & jets, RNG & ran
	){
	size_t first_valid_jet = 0;
	size_t num_valid_jets = jets.size();
	const double R_eff = 5./3.*param_.jet_param.def.R();
	// if there is an unordered jet too far away from the FKL jets
	// then extra gluon constituents of the unordered jet would
	// violate the FKL rapidity ordering
	if((unob_\|\|qqxb_) && jets[0].delta_R(jets[1]) > R_eff){
	++first_valid_jet;
	--num_valid_jets;
	}
	else if((unof_\|\|qqxf_) && jets[jets.size()-1].delta_R(jets[jets.size()-2]) > R_eff){
	--num_valid_jets;
	}
	std::vector<int> np(jets.size(), 1);
	for(int i = 0; i < ng_jets; ++i){
	++np[first_valid_jet + ran.flat() * num_valid_jets];
	}
	weight_ *= std::pow(num_valid_jets, ng_jets);
	return np;
	}

	#ifndef NDEBUG
	namespace{
	bool tagged_FKL_backward(
	std::vector<fastjet::PseudoJet> const & jet_partons
	){
	return std::find_if(
	begin(jet_partons), end(jet_partons),
	[](fastjet::PseudoJet const & p){
	return p.user_index() == backward_FKL_uid;
	}
	) != end(jet_partons);
	}

	bool tagged_FKL_forward(
	std::vector<fastjet::PseudoJet> const & jet_partons
	){
	// the most forward FKL parton is most likely near the end of jet_partons;
	// start search from there
	return std::find_if(
	jet_partons.rbegin(), jet_partons.rend(),
	[](fastjet::PseudoJet const & p){
	return p.user_index() == forward_FKL_uid;
	}
	) != jet_partons.rend();
	}

	bool tagged_FKL_extremal(
	std::vector<fastjet::PseudoJet> const & jet_partons
	){
	return tagged_FKL_backward(jet_partons) && tagged_FKL_forward(jet_partons);
	}

	} // namespace anonymous
	#endif

	std::vector<fastjet::PseudoJet> PhaseSpacePoint::split(
	std::vector<fastjet::PseudoJet> const & jets,
	int ng_jets, size_t qqxbackjet, RNG & ran
	){
	return split(
	jets, distribute_jet_partons(ng_jets, jets, ran), qqxbackjet, ran);
	}

	bool PhaseSpacePoint::pass_extremal_cuts(
	fastjet::PseudoJet const & ext_parton,
	fastjet::PseudoJet const & jet
	) const{
	if(ext_parton.pt() < param_.min_extparton_pt) return false;
	return (ext_parton - jet).pt()/jet.pt() < param_.max_ext_soft_pt_fraction;
	}

	std::vector<fastjet::PseudoJet> PhaseSpacePoint::split(
	std::vector<fastjet::PseudoJet> const & jets,
	std::vector<int> const & np,
	size_t qqxbackjet,
	RNG & ran
	){
	assert(! jets.empty());
	assert(jets.size() == np.size());
	assert(pass_resummation_cuts(jets));

	const size_t most_backward_FKL_idx = 0 + unob_ + qqxb_;
	const size_t most_forward_FKL_idx = jets.size() - 1 - unof_ - qqxf_;
	const auto & jet = param_.jet_param;
	const JetSplitter jet_splitter{jet.def, jet.min_pt};

	std::vector<fastjet::PseudoJet> jet_partons;
	// randomly distribute jet gluons among jets
	for(size_t i = 0; i < jets.size(); ++i){
	auto split_res = jet_splitter.split(jets[i], np[i], ran);
	weight_ *= split_res.weight;
	if(weight_ == 0) return {};
	assert(
	std::all_of(
	begin(split_res.constituents), end(split_res.constituents),
	is_jet_parton
	)
	);
	const auto first_new_parton = jet_partons.insert(
	end(jet_partons),
	begin(split_res.constituents), end(split_res.constituents)
	);
	// mark uno and extremal FKL emissions here so we can check
	// their position once all emissions are generated
	// also mark qqxmid partons, and apply appropriate pt cut.
	auto extremal = end(jet_partons);
	if (i == most_backward_FKL_idx){ //FKL backward emission
	extremal = std::min_element(
	first_new_parton, end(jet_partons), rapidity_less{}
	);
	extremal->set_user_index(backward_FKL_uid);
	}
	else if(((unob_ \|\| qqxb_) && i == 0)){
	// unordered/qqxb
	extremal = std::min_element(
	first_new_parton, end(jet_partons), rapidity_less{}
	);
	extremal->set_user_index((unob_)?unob_uid:qqxb_uid);
	}

	else if (i == most_forward_FKL_idx){
	extremal = std::max_element(
	first_new_parton, end(jet_partons), rapidity_less{}
	);
	extremal->set_user_index(forward_FKL_uid);
	}
	else if(((unof_ \|\| qqxf_) && i == jets.size() - 1)){
	// unordered/qqxf
	extremal = std::max_element(
	first_new_parton, end(jet_partons), rapidity_less{}
	);
	extremal->set_user_index((unof_)?unof_uid:qqxf_uid);
	}
	else if((qqxmid_ && i == qqxbackjet)){
	extremal = std::max_element(
	first_new_parton, end(jet_partons), rapidity_less{}
	);
	extremal->set_user_index(qqxmid1_uid);
	}
	else if((qqxmid_ && i == qqxbackjet+1)){
	extremal = std::min_element(
	first_new_parton, end(jet_partons), rapidity_less{}
	);
	extremal->set_user_index(qqxmid2_uid);
	}
	if(
	extremal != end(jet_partons)
	&& !pass_extremal_cuts(*extremal, jets[i])
	){
	weight_ = 0;
	return {};
	}
	}
	assert(tagged_FKL_extremal(jet_partons));
	std::sort(begin(jet_partons), end(jet_partons), rapidity_less{});
	if(
	!extremal_ok(jet_partons)
	\|\| !split_preserved_jets(jets, jet_partons)
	){
	weight_ = 0.;
	return {};
	}
	return jet_partons;
	}

	bool PhaseSpacePoint::extremal_ok(
	std::vector<fastjet::PseudoJet> const & partons
	) const{
	assert(std::is_sorted(begin(partons), end(partons), rapidity_less{}));
	if(unob_ && partons.front().user_index() != unob_uid) return false;
	if(unof_ && partons.back().user_index() != unof_uid) return false;
	if(qqxb_ && partons.front().user_index() != qqxb_uid) return false;
	if(qqxf_ && partons.back().user_index() != qqxf_uid) return false;
	return
	most_backward_FKL(partons).user_index() == backward_FKL_uid
	&& most_forward_FKL(partons).user_index() == forward_FKL_uid;
	}

	bool PhaseSpacePoint::split_preserved_jets(
	std::vector<fastjet::PseudoJet> const & jets,
	std::vector<fastjet::PseudoJet> const & jet_partons
	) const{
	assert(std::is_sorted(begin(jets), end(jets), rapidity_less{}));

	const auto split_jets = cluster_jets(jet_partons);
	// this can happen if two overlapping jets
	// are both split into more than one parton
	if(split_jets.size() != jets.size()) return false;
	for(size_t i = 0; i < split_jets.size(); ++i){
	// this can happen if there are two overlapping jets
	// and a parton is assigned to the "wrong" jet
	if(!nearby_ep(jets[i].rapidity(), split_jets[i].rapidity(), 1e-2)){
	return false;
	}
	}
	return true;
	}

	template<class Particle>
	Particle const & PhaseSpacePoint::most_backward_FKL(
	std::vector<Particle> const & partons
	) const{
	return partons[0 + unob_ + qqxb_];
	}

	template<class Particle>
	Particle const & PhaseSpacePoint::most_forward_FKL(
	std::vector<Particle> const & partons
	) const{
	const size_t idx = partons.size() - 1 - unof_ - qqxf_;
	assert(idx < partons.size());
	return partons[idx];
	}

	template<class Particle>
	Particle & PhaseSpacePoint::most_backward_FKL(
	std::vector<Particle> & partons
	) const{
	return partons[0 + unob_ + qqxb_];
	}

	template<class Particle>
	Particle & PhaseSpacePoint::most_forward_FKL(
	std::vector<Particle> & partons
	) const{
	const size_t idx = partons.size() - 1 - unof_ - qqxf_;
	assert(idx < partons.size());
	return partons[idx];
	}

	bool PhaseSpacePoint::contains_idx(
	fastjet::PseudoJet const & jet, fastjet::PseudoJet const & parton
	) const {
	auto const & constituents = jet.constituents();
	const int idx = parton.user_index();
	const bool injet = std::find_if(
	begin(constituents), end(constituents),
	[idx](fastjet::PseudoJet const & con){return con.user_index() == idx;}
	) != end(constituents);
	const double minpartonjetpt = 1. - param_.max_ext_soft_pt_fraction;
	return ((parton.pt()>minpartonjetpt*jet.pt())&&injet);
	}

	bool PhaseSpacePoint::jets_ok(
	std::vector<fastjet::PseudoJet> const & Born_jets,
	std::vector<fastjet::PseudoJet> const & partons
	) const{
	fastjet::ClusterSequence cs(partons, param_.jet_param.def);
	const auto jets = sorted_by_rapidity(cs.inclusive_jets(param_.jet_param.min_pt));
	if(jets.size() != Born_jets.size()) return false;
	int in_jet = 0;
	for(size_t i = 0; i < jets.size(); ++i){
	assert(jets[i].has_constituents());
	for(auto && parton: jets[i].constituents()){
	if(is_nonjet_parton(parton)) return false;
	}
	in_jet += jets[i].constituents().size();
	}
	const int expect_in_jet = std::count_if(
	partons.cbegin(), partons.cend(), is_jet_parton
	);
	if(in_jet != expect_in_jet) return false;
	// note that PseudoJet::contains does not work here
	if(! (
	contains_idx(most_backward_FKL(jets), most_backward_FKL(partons))
	&& contains_idx(most_forward_FKL(jets), most_forward_FKL(partons))
	)) return false;
	if(unob_ && !contains_idx(jets.front(), partons.front())) return false;
	if(qqxb_ && !contains_idx(jets.front(), partons.front())) return false;
	if(unof_ && !contains_idx(jets.back(), partons.back())) return false;
	if(qqxf_ && !contains_idx(jets.back(), partons.back())) return false;
	+#ifndef NDEBUG
	for(size_t i = 0; i < jets.size(); ++i){
	assert(nearby_ep(jets[i].rapidity(), Born_jets[i].rapidity(), 1e-2));
	}
	+#endif
	return true;
	}

	void PhaseSpacePoint::reconstruct_incoming(
	std::array<Particle, 2> const & Born_incoming
	){
	std::tie(incoming_[0].p, incoming_[1].p) = incoming_momenta(outgoing_);
	for(size_t i = 0; i < incoming_.size(); ++i){
	incoming_[i].type = Born_incoming[i].type;
	}
	assert(momentum_conserved());
	}

	double PhaseSpacePoint::phase_space_normalisation(
	int num_Born_jets, int num_out_partons
	) const{
	return pow(16*pow(M_PI,3), num_Born_jets - num_out_partons);
	}

	bool PhaseSpacePoint::momentum_conserved() const{
	fastjet::PseudoJet diff;
	for(auto const & in: incoming()) diff += in.p;
	const double norm = diff.E();
	for(auto const & out: outgoing()) diff -= out.p;
	return nearby(diff, fastjet::PseudoJet{}, norm);
	}

	} //namespace HEJ
	diff --git a/src/resummation_jet.cc b/src/resummation_jet.cc
	index f51ba8d..9f94c1d 100644
	--- a/src/resummation_jet.cc
	+++ b/src/resummation_jet.cc
	@@ -1,112 +1,113 @@
	/**
	* \authors The HEJ collaboration (see AUTHORS for details)
	* \date 2019
	* \copyright GPLv2 or later
	*/
	#include "HEJ/resummation_jet.hh"

	#include <assert.h>
	#include <math.h>
	#include <stdio.h>

	#include <boost/numeric/ublas/lu.hpp>
	#include <boost/numeric/ublas/matrix.hpp>

	#include "fastjet/PseudoJet.hh"

	#include "HEJ/utility.hh"

	namespace HEJ{

	std::vector<fastjet::PseudoJet> resummation_jet_momenta(
	std::vector<fastjet::PseudoJet> const & p_born,
	fastjet::PseudoJet const & qperp
	) {
	// for "new" reshuffling p^B = p + qperp*\|p^B\|/P^B
	double Pperp_born = 0.;
	for(auto const & p: p_born) Pperp_born += p.perp();

	std::vector<fastjet::PseudoJet> p_res;
	p_res.reserve(p_born.size());
	for(auto & pB: p_born) {
	const double px = pB.px() - qperp.px()*pB.perp()/Pperp_born;
	const double py = pB.py() - qperp.py()*pB.perp()/Pperp_born;
	const double pperp = sqrt(pxpx + pypy);
	// keep the rapidities fixed
	const double pz = pperp*sinh(pB.rapidity());
	const double E = pperp*cosh(pB.rapidity());
	p_res.emplace_back(px, py, pz, E);
	assert(
	HEJ::nearby_ep(
	p_res.back().rapidity(),
	pB.rapidity(),
	1e-5
	)
	);
	}
	return p_res;
	}

	namespace{
	enum coordinates : size_t {
	x1, x2
	};

	namespace ublas = boost::numeric::ublas;

	template<class Matrix>
	double det(ublas::matrix_expression<Matrix> const& m) {

	ublas::permutation_matrix<size_t> pivots{m().size1()};
	Matrix mLu{m()};

	const auto is_singular = lu_factorize(mLu, pivots);

	if(is_singular) return 0.;

	double det = 1.0;
	for (std::size_t i = 0; i < pivots.size(); ++i){
	if (pivots(i) != i) det = -det;

	det *= mLu(i,i);
	}

	return det;
	}

	using ublas::matrix;
	}

	double resummation_jet_weight(
	std::vector<fastjet::PseudoJet> const & p_born,
	fastjet::PseudoJet const & qperp
	) {

	static constexpr int num_coordinates = 2;
	auto Jacobian = matrix<double>{
	num_coordinates*p_born.size(),
	num_coordinates*p_born.size()
	};
	double P_perp = 0.;
	for(auto const & J: p_born) P_perp += J.perp();

	for(size_t l = 0; l < p_born.size(); ++l){
	const double Jl_perp = p_born[l].perp();
	for(size_t lp = 0; lp < p_born.size(); ++lp){
	- const int delta_l = l == lp;
	- const double Jlp_perp = p_born[lp].perp();
	+ const int delta_l = (l == lp);
	+ const auto & Jlp = p_born[lp];
	+ const double Jlp_perp = Jlp.perp();
	for(size_t x = x1; x <= x2; ++x){
	+ const double qxy = (x==x1)?qperp.px():qperp.py();
	for(size_t xp = x1; xp <= x2; ++xp){
	+ const double Jxy = (xp==x1)?Jlp.px():Jlp.py();
	const int delta_x = x == xp;
	Jacobian(2l + x, 2lp + xp) =
	+ delta_l*delta_x
	- - qperp[x]p_born[lp][xp]/(P_perpJlp_perp)*(
	- + delta_l - Jl_perp/P_perp
	- );
	+ - qxyJxy/(P_perpJlp_perp) * (delta_l - Jl_perp/P_perp);
	}
	}
	}
	}
	return det(Jacobian);
	}
	}

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