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diff --git a/include/HEJ/EventReweighter.hh b/include/HEJ/EventReweighter.hh
index 3d4455a..657fdfa 100644
--- a/include/HEJ/EventReweighter.hh
+++ b/include/HEJ/EventReweighter.hh
@@ -1,199 +1,199 @@
/** \file
* \brief Declares the EventReweighter class
*
* EventReweighter is the main class used within HEJ 2. It reweights the
* resummation events.
*
* \authors The HEJ collaboration (see AUTHORS for details)
* \date 2019
* \copyright GPLv2 or later
*/
#pragma once
#include <array>
#include <functional>
#include <utility>
#include <vector>
#include "HEJ/config.hh"
#include "HEJ/event_types.hh"
#include "HEJ/MatrixElement.hh"
#include "HEJ/Parameters.hh"
#include "HEJ/PDF.hh"
#include "HEJ/PDG_codes.hh"
#include "HEJ/RNG.hh"
#include "HEJ/ScaleFunction.hh"
#include "HEJ/StatusCode.hh"
namespace LHEF {
class HEPRUP;
}
namespace HEJ{
class Event;
//! Beam parameters
/**
* Currently, only symmetric beams are supported,
* so there is a single beam energy.
*/
struct Beam{
double E; /**< Beam energy */
std::array<ParticleID, 2> type; /**< Beam particles */
};
//! Main class for reweighting events in HEJ.
class EventReweighter{
using EventType = event_type::EventType;
public:
EventReweighter(
Beam beam, /**< Beam Energy */
int pdf_id, /**< PDF ID */
ScaleGenerator scale_gen, /**< Scale settings */
EventReweighterConfig conf, /**< Configuration parameters */
HEJ::RNG & ran /**< Random number generator */
);
EventReweighter(
LHEF::HEPRUP const & heprup, /**< LHEF event header */
ScaleGenerator scale_gen, /**< Scale settings */
EventReweighterConfig conf, /**< Configuration parameters */
HEJ::RNG & ran /**< Random number generator */
);
//! Get the used pdf
PDF const & pdf() const;
//! Generate resummation events for a given fixed-order event
/**
* @param ev Fixed-order event corresponding
* to the resummation events
* @param num_events Number of trial resummation configurations.
* @returns A vector of resummation events.
*
* The result vector depends on the type of the input event and the
* treatment of different types as specified in the constructor:
*
* \ref reweight The result vector contains between
* 0 and num_events resummation events.
*
* \ref keep If the input event passes the resummation jet cuts
* the result vector contains one event. Otherwise it is empty.
*
* \ref discard The result vector is empty
*/
std::vector<Event> reweight(
Event const & ev,
int num_events
);
//! Gives all StatusCodes of the last reweight()
/**
* Each StatusCode corresponds to one tried generation. Only good
* StatusCodes generated an event.
*/
std::vector<StatusCode> const & status() const {
return status_;
}
private:
template<typename... T>
PDF const & pdf(T&& ...);
/** \internal
* \brief main generation/reweighting function:
* generate phase space points and divide out Born factors
*/
std::vector<Event> gen_res_events(
- Event const & ev, int num_events
+ Event const & ev, size_t num_events
);
std::vector<Event> rescale(
Event const & Born_ev, std::vector<Event> events
) const;
/** \internal
* \brief Do the Jets pass the resummation Cuts?
*
* @param ev Event in Question
* @returns 0 or 1 depending on if ev passes Jet Cuts
*/
bool jets_pass_resummation_cuts(Event const & ev) const;
/** \internal
* \brief pdf_factors Function
*
* @param ev Event in Question
* @returns EventFactor due to PDFs
*
* Calculates the Central value and the variation due
* to the PDF choice made.
*/
Weights pdf_factors(Event const & ev) const;
/** \internal
* \brief matrix_elements Function
*
* @param ev Event in question
* @returns EventFactor due to MatrixElements
*
* Calculates the Central value and the variation due
* to the Matrix Element.
*/
Weights matrix_elements(Event const & ev) const;
/** \internal
* \brief Scale-dependent part of fixed-order matrix element
*
* @param ev Event in question
* @returns EventFactor scale variation due to FO-ME.
*
* This is only called to compute the scale variation for events where
* we don't do resummation (e.g. non-FKL).
* Since at tree level the scale dependence is just due to alpha_s,
* it is enough to return the alpha_s(mur) factors in the matrix element.
* The rest drops out in the ratio of (output event ME)/(input event ME),
* so we never have to compute it.
*/
Weights fixed_order_scale_ME(Event const & ev) const;
/** \internal
* \brief Computes the tree level matrix element
*
* @param ev Event in Question
* @returns HEJ approximation to Tree level Matrix Element
*
* This computes the HEJ approximation to the tree level FO
* Matrix element which is used within the LO weighting process.
*/
double tree_matrix_element(Event const & ev) const;
//! \internal General parameters
EventReweighterConfig param_;
//! \internal Beam energy
double E_beam_;
//! \internal PDF
PDF pdf_;
//! \internal Object to calculate the square of the matrix element
MatrixElement MEt2_;
//! \internal Object to calculate event renormalisation and factorisation scales
ScaleGenerator scale_gen_;
/** \internal random number generator
*
* \note We use a reference_wrapper so that EventReweighter objects can
* still be copied (which would be impossible with a reference).
*/
std::reference_wrapper<HEJ::RNG> ran_;
std::vector<StatusCode> status_;
};
template<typename... T>
PDF const & EventReweighter::pdf(T&&... t){
return pdf_ = PDF{std::forward<T>(t)...};
}
}
diff --git a/src/EventReweighter.cc b/src/EventReweighter.cc
index 261807b..7a26440 100644
--- a/src/EventReweighter.cc
+++ b/src/EventReweighter.cc
@@ -1,275 +1,275 @@
/**
* \authors The HEJ collaboration (see AUTHORS for details)
* \date 2019
* \copyright GPLv2 or later
*/
#include "HEJ/EventReweighter.hh"
#include <algorithm>
#include <assert.h>
#include <limits>
#include <math.h>
#include <stddef.h>
#include <string>
#include <unordered_map>
#include "fastjet/ClusterSequence.hh"
#include "LHEF/LHEF.h"
#include "HEJ/Event.hh"
#include "HEJ/exceptions.hh"
#include "HEJ/Particle.hh"
#include "HEJ/PDG_codes.hh"
#include "HEJ/PhaseSpacePoint.hh"
namespace HEJ{
using EventType = event_type::EventType;
namespace {
static_assert(
std::numeric_limits<double>::has_quiet_NaN,
"no quiet NaN for double"
);
constexpr double NaN = std::numeric_limits<double>::quiet_NaN();
Event::EventData to_EventData(PhaseSpacePoint const & psp){
Event::EventData result;
result.incoming=psp.incoming();
assert(result.incoming.size() == 2);
result.outgoing=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),
rapidity_less{}
)
);
assert(result.outgoing.size() >= 2);
result.decays = psp.decays();
result.parameters.central = {NaN, NaN, psp.weight()};
return result;
}
} // namespace anonymous
EventReweighter::EventReweighter(
LHEF::HEPRUP const & heprup,
ScaleGenerator scale_gen,
EventReweighterConfig conf,
HEJ::RNG & ran
):
EventReweighter{
HEJ::Beam{
heprup.EBMUP.first,
{{
static_cast<HEJ::ParticleID>(heprup.IDBMUP.first),
static_cast<HEJ::ParticleID>(heprup.IDBMUP.second)
}}
},
heprup.PDFSUP.first,
std::move(scale_gen),
std::move(conf),
ran
}
{
if(heprup.EBMUP.second != E_beam_){
throw std::invalid_argument(
"asymmetric beam: " + std::to_string(E_beam_)
+ " ---> <--- " + std::to_string(heprup.EBMUP.second)
);
};
if(heprup.PDFSUP.second != pdf_.id()){
throw std::invalid_argument(
"conflicting PDF ids: " + std::to_string(pdf_.id())
+ " vs. " + std::to_string(heprup.PDFSUP.second)
);
}
}
EventReweighter::EventReweighter(
Beam beam,
int pdf_id,
ScaleGenerator scale_gen,
EventReweighterConfig conf,
HEJ::RNG & ran
):
param_{std::move(conf)},
E_beam_{beam.E},
pdf_{pdf_id, beam.type.front(), beam.type.back()},
MEt2_{
[this](double mu){ return pdf_.Halphas(mu); },
param_.ME_config
},
scale_gen_(std::move(scale_gen)),
ran_{ran}
{}
PDF const & EventReweighter::pdf() const{
return pdf_;
}
std::vector<Event> EventReweighter::reweight(
Event const & input_ev, int num_events
){
auto res_events = gen_res_events(input_ev, num_events);
if(res_events.empty()) return {};
for(auto & event: res_events) event = scale_gen_(event);
return rescale(input_ev, std::move(res_events));
}
std::vector<Event> EventReweighter::gen_res_events(
Event const & ev,
- int phase_space_points
+ size_t phase_space_points
){
assert(ev.variations().empty());
status_.clear();
switch(param_.treat.at(ev.type())){
case EventTreatment::discard: {
status_.emplace_back(StatusCode::discard);
return {};
}
case EventTreatment::keep:
if(! jets_pass_resummation_cuts(ev)) {
status_.emplace_back(StatusCode::failed_resummation_cuts);
return {};
}
else {
status_.emplace_back(StatusCode::good);
return {ev};
}
default:;
}
const double Born_shat = shat(ev);
std::vector<Event> resummation_events;
status_.reserve(phase_space_points);
- for(int psp_number = 0; psp_number < phase_space_points; ++psp_number){
+ for(size_t psp_number = 0; psp_number < phase_space_points; ++psp_number){
PhaseSpacePoint psp{ev, param_.psp_config, ran_};
status_.emplace_back(psp.status());
assert(psp.status() != StatusCode::unspecified);
if(psp.status() != StatusCode::good) continue;
assert(psp.weight() != 0.);
if(psp.incoming()[0].E() > E_beam_ || psp.incoming()[1].E() > E_beam_) {
status_.back() = StatusCode::too_much_energy;
continue;
}
resummation_events.emplace_back(
to_EventData( std::move(psp) ).cluster(
param_.jet_param.def, param_.jet_param.min_pt
)
);
auto & new_event = resummation_events.back();
if( new_event.type() != ev.type() )
throw std::logic_error{"Resummation Event does not match Born event"};
new_event.generate_colours(ran_);
assert(new_event.variations().empty());
new_event.central().mur = ev.central().mur;
new_event.central().muf = ev.central().muf;
const double resum_shat = shat(new_event);
new_event.central().weight *= ev.central().weight*Born_shat*Born_shat/
(phase_space_points*resum_shat*resum_shat);
}
return resummation_events;
}
std::vector<Event> EventReweighter::rescale(
Event const & Born_ev,
std::vector<Event> events
) const{
const double Born_pdf = pdf_factors(Born_ev).central;
const double Born_ME = tree_matrix_element(Born_ev);
for(auto & cur_event: events){
const auto pdf = pdf_factors(cur_event);
assert(pdf.variations.size() == cur_event.variations().size());
const auto ME = matrix_elements(cur_event);
assert(ME.variations.size() == cur_event.variations().size());
cur_event.parameters() *= pdf*ME/(Born_pdf*Born_ME);
}
return events;
};
bool EventReweighter::jets_pass_resummation_cuts(
Event const & ev
) const{
const auto out_as_PseudoJet = to_PseudoJet(filter_partons(ev.outgoing()));
fastjet::ClusterSequence cs{out_as_PseudoJet, param_.jet_param.def};
return cs.inclusive_jets(param_.jet_param.min_pt).size() == ev.jets().size();
}
Weights EventReweighter::pdf_factors(Event const & ev) const{
auto const & a = ev.incoming().front();
auto const & b = ev.incoming().back();
const double xa = a.p.e()/E_beam_;
const double xb = b.p.e()/E_beam_;
Weights result;
std::unordered_map<double, double> known_pdf;
result.central =
pdf_.pdfpt(0,xa,ev.central().muf,a.type)*
pdf_.pdfpt(1,xb,ev.central().muf,b.type);
known_pdf.emplace(ev.central().muf, result.central);
result.variations.reserve(ev.variations().size());
for(auto const & ev_param: ev.variations()){
const double muf = ev_param.muf;
auto cur_pdf = known_pdf.find(muf);
if(cur_pdf == known_pdf.end()){
cur_pdf = known_pdf.emplace(
muf,
pdf_.pdfpt(0,xa,muf,a.type)*pdf_.pdfpt(1,xb,muf,b.type)
).first;
}
result.variations.emplace_back(cur_pdf->second);
}
assert(result.variations.size() == ev.variations().size());
return result;
}
Weights
EventReweighter::matrix_elements(Event const & ev) const{
assert(param_.treat.count(ev.type()) > 0);
if(param_.treat.find(ev.type())->second == EventTreatment::keep){
return fixed_order_scale_ME(ev);
}
return MEt2_(ev);
}
double EventReweighter::tree_matrix_element(Event const & ev) const{
assert(ev.variations().empty());
assert(param_.treat.count(ev.type()) > 0);
if(param_.treat.find(ev.type())->second == EventTreatment::keep){
return fixed_order_scale_ME(ev).central;
}
return MEt2_.tree(ev).central;
}
Weights
EventReweighter::fixed_order_scale_ME(Event const & ev) const{
int alpha_s_power = 0;
for(auto const & part: ev.outgoing()){
if(is_parton(part))
++alpha_s_power;
else if(part.type == pid::Higgs) {
alpha_s_power += 2;
}
// nothing to do for other uncoloured particles
}
Weights result;
result.central = pow(pdf_.Halphas(ev.central().mur), alpha_s_power);
for(auto const & var: ev.variations()){
result.variations.emplace_back(
pow(pdf_.Halphas(var.mur), alpha_s_power)
);
}
return result;
}
} // namespace HEJ

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