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# See the POD documentation at the end of this
# document for detailed copyright information.
# (c) 2002-2003 Steffen Mueller, all rights reserved.

package Physics::Particles;

use 5.006;
use strict;
use warnings;

use constant C_VACUUM         => 299792458;
use constant C_VACUUM_SQUARED => 299792458 * 299792458;

use Carp;

use Data::Dumper;

use vars qw/$VERSION/;
$VERSION = '1.02';


# constructor new
# 
# Does not require any arguments. All arguments
# directly modify the object as key/value pairs.
# returns freshly created simulator object.

sub new {
	my $proto = shift;
	my $class = ref $proto || $proto;

	# Make a new object with default values.
	my $self = {
		forces => [], # All forces (callbacks) will be stored here.
		p      => [], # All particles (hashrefs) will be stored here.
		p_attr => {
			x => 0,
			y => 0,
			z => 0,
			vx => 0,
			vy => 0,
			vz => 0,
			m => 1,
			n => '',
		},
		@_
	};

	bless $self => $class;
}


# method set_particle_default
#
# Takes a hash reference whichis then used as is for
# particle default attributes such as position, velocity, mass,
# unique ID, or whatever properties you fancy.

sub set_particle_default {
	my $self = shift;
	my $hashref = shift;
	
	ref $hashref eq 'HASH'
	  or croak "Must pass hash reference to set_particle_default().";
	
	$self->{p_attr} = $hashref;
	return 1;
}

# method add_particle
# 
# Takes key/value pairs of particle attributes.
# Attributes default to whatever has been set using
# set_particle_default.
# A new particle represented by the attributes is then
# created in the simulation and its particle number is
# returned. Attributes starting with an underscore are
# reserved to internal attributes (so don't use any of them).

sub add_particle {
	my $self = shift;
	
	my $particle = {
		%{$self->{p_attr}},
		@_,
		_fx => 0,
		_fy => 0,
		_fz => 0,
	};
	
	my $particle_no = $self->_make_particle();
	
	$self->{p}[$particle_no] = $particle;
	
	return $particle_no;
}


# private method _make_particle
#
# Returns a currently unused particle number or
# appends an empty particle to the particle list.

sub _make_particle {
	my $self = shift;
	my $count = 0;
	foreach (@{$self->{p}}) {
		return $count unless ref $_;
		$count++;