Loading...
Searching...
No Matches
MinHeap.cc
//FJSTARTHEADER
// $Id$
//
// Copyright (c) 2005-2021, Matteo Cacciari, Gavin P. Salam and Gregory Soyez
//
//----------------------------------------------------------------------
// This file is part of FastJet.
//
// FastJet is free software; you can redistribute it and/or modify
// it under the terms of the GNU General Public License as published by
// the Free Software Foundation; either version 2 of the License, or
// (at your option) any later version.
//
// The algorithms that underlie FastJet have required considerable
// development. They are described in the original FastJet paper,
// hep-ph/0512210 and in the manual, arXiv:1111.6097. If you use
// FastJet as part of work towards a scientific publication, please
// quote the version you use and include a citation to the manual and
// optionally also to hep-ph/0512210.
//
// FastJet is distributed in the hope that it will be useful,
// but WITHOUT ANY WARRANTY; without even the implied warranty of
// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
// GNU General Public License for more details.
//
// You should have received a copy of the GNU General Public License
// along with FastJet. If not, see <http://www.gnu.org/licenses/>.
//----------------------------------------------------------------------
//FJENDHEADER
#include "fastjet/internal/MinHeap.hh"
#include<iostream>
#include<cmath>
#include<limits>
FASTJET_BEGIN_NAMESPACE // defined in fastjet/internal/base.hh
using namespace std;
//----------------------------------------------------------------------
/// construct the MinHeap; structure will be as follows:
/// . _heap[0].minloc points to globally smallest entry
/// _heap[1].minloc points to smallest entry in one half of heap
/// _heap[2].minloc points to smallest entry in other half of heap
///
/// . for _heap[i], the "parent" is to be found at (i-1)/2
void MinHeap::initialise(const std::vector<double> & values){
// fill the high-range of the heap with the largest possible value
// (minloc of each entry is itself)
for (unsigned i = values.size(); i < _heap.size(); i++) {
_heap[i].value = std::numeric_limits<double>::max();
_heap[i].minloc = &(_heap[i]);
}
// fill the rest of the heap with the actual values
// (minloc of each entry is itself)
for (unsigned i = 0; i < values.size(); i++) {
_heap[i].value = values[i];
_heap[i].minloc = &(_heap[i]);
}
// now adjust the minlocs so that everything is OK...
for (unsigned i = _heap.size()-1; i > 0; i--) {
ValueLoc * parent = &(_heap[(i-1)/2]);
ValueLoc * here = &(_heap[i]);
if (here->minloc->value < parent->minloc->value) {
parent->minloc = here->minloc;
}
}
//cout << minloc() << " "<<sqrt(minval())<<endl;
//cout << sqrt(_heap[47].value)<<endl;
//cout << sqrt(_heap[48].value)<<endl;
//cout << sqrt(_heap[25].value)<<endl;
}
//----------------------------------------------------------------------
void MinHeap::update(unsigned int loc, double new_value) {
assert(loc < _heap.size());
ValueLoc * start = &(_heap[loc]);
// if the minloc is somewhere below us and our value is no smaller
// than the previous value, we can't possibly change the minloc
if (start->minloc != start && !(new_value < start->minloc->value)) {
start->value = new_value;
//std::cout << " had easy exit\n";
return;
}
// update the value and put a temporary location
start->value = new_value;
start->minloc = start;
// warn that a change has been made at this place
bool change_made = true;
// to make sure we don't go off edge...
ValueLoc * heap_end = (&(_heap[0])) + _heap.size();
// now work our way up the heap
while(change_made) {
ValueLoc * here = &(_heap[loc]);
change_made = false;
// if we were pointing to start, then we must re-initialise things
if (here->minloc == start) {
here->minloc = here; change_made = true;
}
// now compare current location to children (at 2*loc+1, 2*loc+2)
//ValueLoc * child = &(_heap[2*loc+1]);
// GPS 2020-04-07: changed the way the following line
// is expressed, so as to work around issue reported by
// Andrii Verbyitskyi where compilation with gcc's
// -D_GLIBCXX_ASSERTIONS=1 -D_GLIBCXX_SANITIZE_VECTOR=1
// results in a crash because the compiler thinks we
// are accessing the vector at a location that is sometimes
// invalid, whereas we are just getting the address
ValueLoc * child = &(_heap[0]) + (2*loc+1);
if (child < heap_end && child->minloc->value < here->minloc->value ) {
here->minloc = child->minloc;
change_made = true;}
child++;
if (child < heap_end && child->minloc->value < here->minloc->value ) {
here->minloc = child->minloc;
change_made = true;}
// then we move up (loc ->(loc-1)/2) if there's anywhere to go
if (loc == 0) {break;}
loc = (loc-1)/2;
}
}
FASTJET_END_NAMESPACE
fastjet::MinHeap::update
void update(unsigned int, double)
update the value at the specified location
Definition MinHeap.cc:79
fastjet::MinHeap::minloc
unsigned int minloc() const
return the location of the minimal value on the heap
Definition MinHeap.hh:69
fastjet::MinHeap::initialise
void initialise(const std::vector< double > &values)
initialise the heap with the supplied values.
Definition MinHeap.cc:47