package Chemistry::Atom;
$VERSION = '0.37';
# $Id: Atom.pm,v 1.44 2009/05/10 19:37:58 itubert Exp $
=head1 NAME
Chemistry::Atom - Chemical atoms as objects in molecules
=head1 SYNOPSIS
use Chemistry::Atom;
my $atom = new Chemistry::Atom(
id => 'a1',
coords => [$x, $y, $z],
symbol => 'Br'
);
print $atom->print;
=head1 DESCRIPTION
This module includes objects to describe chemical atoms.
An atom is defined by its symbol and its coordinates, among other attributes.
Atomic coordinates are described by a Math::VectorReal
object, so that they can be easily used in vector operations.
=head2 Atom Attributes
In addition to common attributes such as id, name, and type,
atoms have the following attributes, which are accessed or
modified through methods defined below: bonds, coords, internal_coords,
Z, symbol, etc.
In general, to get the value of a property, use $atom->method without
any parameters. To set the value, use $atom->method($new_value). When setting
an attribute, the accessor returns the atom object, so that accessors can be
chained:
$atom->symbol("C")->name("CA")->coords(1,2,3);
=cut
# Considering to add the following attributes:
# mass_number (A)
use 5.006;
use strict;
use warnings;
use Scalar::Util 'weaken';
use Math::VectorReal qw(O vector);
use Math::Trig;
use Carp;
use base qw(Chemistry::Obj Exporter);
use List::Util qw(first);
our @EXPORT_OK = qw(distance angle dihedral angle_deg dihedral_deg);
our %EXPORT_TAGS = (
all => \@EXPORT_OK,
);
my $N = 0; # Number of atoms created so far, used to generate default IDs.
our @ELEMENTS = qw(
n
H He
Li Be B C N O F Ne
Na Mg Al Si P S Cl Ar
K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr
Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe
Cs Ba
La Ce Pr Nd Pm Sm Eu Gd Tb Dy Ho Er Tm Yb
Lu Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn
Fr Ra
Ac Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No
Lr Rf Db Sg Bh Hs Mt Ds Uuu Uub Uut Uuq Uup Uuh Uus Uuo
);
our %ELEMENTS;
for (my $i = 1; $i < @ELEMENTS; ++$i){
$ELEMENTS{$ELEMENTS[$i]} = $i;
}
$ELEMENTS{D} = $ELEMENTS{T} = 1;
my %Atomic_masses = (
"H" => 1.00794, "D" => 2.014101, "T" => 3.016049, "He" => 4.002602,
"Li" => 6.941, "Be" => 9.012182, "B" => 10.811, "C" => 12.0107,
"N" => 14.00674, "O" => 15.9994, "F" => 18.9984032, "Ne" => 20.1797,
"Na" => 22.989770, "Mg" => 24.3050, "Al" => 26.981538, "Si" => 28.0855,
"P" => 30.973761, "S" => 32.066, "Cl" => 35.4527, "Ar" => 39.948,
"K" => 39.0983, "Ca" => 40.078, "Sc" => 44.955910, "Ti" => 47.867,
"V" => 50.9415, "Cr" => 51.9961, "Mn" => 54.938049, "Fe" => 55.845,
"Co" => 58.933200, "Ni" => 58.6934, "Cu" => 63.546, "Zn" => 65.39,
"Ga" => 69.723, "Ge" => 72.61, "As" => 74.92160, "Se" => 78.96,
"Br" => 79.904, "Kr" => 83.80, "Rb" => 85.4678, "Sr" => 87.62,
"Y" => 88.90585, "Zr" => 91.224, "Nb" => 92.90638, "Mo" => 95.94,
"Tc" => 98, "Ru" => 101.07, "Rh" => 102.90550, "Pd" => 106.42,
"Ag" => 107.8682, "Cd" => 112.411, "In" => 114.818, "Sn" => 118.710,
"Sb" => 121.760, "Te" => 127.60, "I" => 126.90447, "Xe" => 131.29,
"Cs" => 132.90545, "Ba" => 137.327, "La" => 138.9055, "Ce" => 140.116,
"Pr" => 140.90765, "Nd" => 144.24, "Pm" => 145, "Sm" => 150.36,
"Eu" => 151.964, "Gd" => 157.25, "Tb" => 158.92534, "Dy" => 162.50,
"Ho" => 164.93032, "Er" => 167.26, "Tm" => 168.93421, "Yb" => 173.04,
"Lu" => 174.967, "Hf" => 178.49, "Ta" => 180.9479, "W" => 183.84,
"Re" => 186.207, "Os" => 190.23, "Ir" => 192.217, "Pt" => 195.078,
"Au" => 196.96655, "Hg" => 200.59, "Tl" => 204.3833, "Pb" => 207.2,
"Bi" => 208.98038, "Po" => 209, "At" => 210, "Rn" => 222,
"Fr" => 223, "Ra" => 226, "Ac" => 227, "Th" => 232.038,
"Pa" => 231.03588, "U" => 238.0289, "Np" => 237, "Pu" => 244,
"Am" => 243, "Cm" => 247, "Bk" => 247, "Cf" => 251,
"Es" => 252, "Fm" => 257, "Md" => 258, "No" => 259,
"Lr" => 262, "Rf" => 261, "Db" => 262, "Sg" => 266,
"Bh" => 264, "Hs" => 269, "Mt" => 268, "Ds" => 271,
);
=head1 METHODS
=over 4
=item Chemistry::Atom->new(name => value, ...)
Create a new Atom object with the specified attributes.
=cut
sub new {
my $class = shift;
my %args = @_;
my $self = bless {
id => $class->nextID(),
coords => vector(0, 0, 0),
Z => 0,
symbol => '',
bonds => [],
}, $class;
$self->$_($args{$_}) for (keys %args);
$self;
}
sub nextID {
"a".++$N;
}
sub reset_id {
$N = 0;
}
=item $atom->Z($new_Z)
Sets and returns the atomic number (Z). If the symbol of the atom doesn't
correspond to a known element, Z = undef.
=cut
sub Z {
my $self = shift;
if(@_) {
$self->{symbol} = $ELEMENTS[$_[0]];
$self->{Z} = $_[0];
return $self;
} else {
return $self->{Z};
}
}
=item $atom->symbol($new_symbol)
Sets and returns the atomic symbol.
=cut
sub symbol {
my $self = shift;
if(@_) {
my $symbol = shift;
$symbol =~ s/ //g;
$self->{Z} = $ELEMENTS{$symbol};
$self->{symbol} = $symbol;
return $self;
} else {
return $self->{symbol};
}
}
=item $atom->mass($new_mass)
Sets and returns the atomic mass in atomic mass units. Any arbitrary mass may
be set explicitly by using this method. However, if no mass is set explicitly
and this method is called as an accessor, the return value is the following:
1) If the mass number is undefined (see the mass_number method below), the
relative atomic mass from the 1995 IUPAC recommendation is used. (Table stolen
from the Chemistry::MolecularMass module by Maksim A. Khrapov).
2) If the mass number is defined and the L<Chemistry::Isotope> module is
available and it knows the mass for the isotope, the exact mass of the isotope
is used; otherwise, the mass number is returned.
=cut
sub mass {
my $self = shift;
if (@_) {
$self->{mass} = shift;
return $self;
} else {
if (defined $self->{mass}) {
return $self->{mass};
} elsif (defined $self->{mass_number}) {
if (eval { require Chemistry::Isotope } and
my $m = Chemistry::Isotope::isotope_mass(
$self->{mass_number}, $self->{Z})
) {
return $m;
} else {
return $self->{mass_number};
}
} else {
return $Atomic_masses{$self->symbol};
}
}
}
=item $atom->mass_number($new_mass_number)
Sets or gets the mass number. The mass number is undefined unless is
set explicitly (this module does not try to guess a default mass number based
on the natural occurring isotope distribution).
=cut
Chemistry::Obj::accessor('mass_number');
=item $atom->coords
my $vector = $atom->coords; # get a Math::VectorReal object
$atom->coords($vector); # set a Math::VectorReal object
$atom->coords([$x, $y, $z]); # also accepts array refs
$atom->coords($x, $y, $z); # also accepts lists
Sets or gets the atom's coordinates. It can take as a parameter a
Math::VectorReal object, a reference to an array, or the list of coordinates.
=cut
sub coords {
my $self = shift;
if(@_) {
if (UNIVERSAL::isa($_[0], "Math::VectorReal")) {
$self->{coords} = $_[0];
} elsif (ref $_[0] eq "ARRAY") {
$self->{coords} = vector(@{$_[0]});
} else {
$self->{coords} = vector(@_);
}
} else {
return $self->{coords};
}
$self;
}
=item $atom->internal_coords
# get a Chemistry::InternalCoords object
my $ic = $atom->internal_coords;
# set a Chemistry::InternalCoords object
$atom->internal_coords($vic);
# also accepts array refs
$atom->internal_coords([8, 1.54, 7, 109.47, 6, 120.0]);
# also accepts lists
$atom->internal_coords(8, 1.54, 7, 109.47, 6, 120.0);
Sets or gets the atom's internal coordinates. It can take as a parameter a
Chemistry::InternalCoords object, a reference to an array, or the list of
coordinates. In the last two cases, the list elements are the following: atom
number or reference for distance, distance, atom number or reference for angle,
angle in degrees, atom number or reference for dihedral, dihedral in degrees.
=cut
sub internal_coords {
my $self = shift;
if(@_) {
if (UNIVERSAL::isa($_[0], "Chemistry::InternalCoords")) {
$self->{internal_coords} = $_[0];
} elsif (ref $_[0] eq "ARRAY") {
require Chemistry::InternalCoords;
$self->{internal_coords} =
Chemistry::InternalCoords->new($self, @{$_[0]});
} else {
require Chemistry::InternalCoords;
$self->{internal_coords} =
Chemistry::InternalCoords->new($self, @_);
}
} else {
return $self->{internal_coords};
}
$self;
}
=item $atom->x3, $atom->y3, $atom->z3
Get the x, y or z 3D coordinate of the atom. This methods are just accessors
that don't change the coordinates. $atom->x3 is short for
($atom->coords->array)[0], and so on.
=cut
sub x3 { ($_[0]->coords->array)[0] }
sub y3 { ($_[0]->coords->array)[1] }
sub z3 { ($_[0]->coords->array)[2] }
=item $atom->formal_charge($charge)
Set or get the formal charge of the atom.
=cut
Chemistry::Obj::accessor('formal_charge');
=item $atom->formal_radical($radical)
Set or get the formal radical multiplicity for the atom.
=cut
Chemistry::Obj::accessor('formal_radical');
=item $atom->implicit_hydrogens($h_count)
Set or get the number of implicit hydrogen atoms bonded to the atom.
=cut
sub implicit_hydrogens { shift->hydrogens(@_) }
=item $atom->hydrogens($h_count)
Set or get the number of implicit hydrogen atoms bonded to the atom
(DEPRECATED: USE C<implicit_hydrogens> INSTEAD).
=cut
Chemistry::Obj::accessor('hydrogens');
=item $atom->total_hydrogens($h_count)
Get the total number of hydrogen atoms bonded to the atom (implicit +
explicit).
=cut
sub total_hydrogens {
my ($self) = @_;
no warnings 'uninitialized';
$self->hydrogens + grep { $_->symbol eq 'H' } $self->neighbors;
}
=item $atom->sprout_hydrogens
Convert all the implicit hydrogens for this atom to explicit hydrogens. Note:
it does B<not> generate coordinates for the new atoms.
=cut
sub sprout_hydrogens {
my ($self) = @_;
for (1 .. $self->implicit_hydrogens || 0) {
$self->parent->new_bond(
atoms => [$self, $self->parent->new_atom(symbol => 'H')]);
}
$self->implicit_hydrogens(0);
}
=item $atom->collapse_hydrogens
Delete neighboring hydrogen atoms and add them as implicit hydrogens for this
atom.
=cut
sub collapse_hydrogens {
my ($self) = @_;
no warnings 'uninitialized';
my $implicit = $self->implicit_hydrogens;
for my $nei ($self->neighbors) {
$nei->delete, $implicit++ if $nei->symbol eq 'H';
}
$self->implicit_hydrogens($implicit);
}
my %VALENCE_TABLE = (
Br => 1, Cl => 1, B => 3, C => 4, N => 3, O => 2, P => 3, S => 2,
F => 1, I => 1,
);
# to make it easier to test
sub _calc_implicit_hydrogens {
my ($self, $symbol, $valence, $charge, $radical) = @_;
no warnings 'uninitialized';
my $h_count = $VALENCE_TABLE{$symbol} - $valence;
# should account for non-kekulized aromatic bonds
# some common charge situations
if (($symbol =~ /^(?:[NOSFI]|Cl|Br)$/) && $charge == -1) {
$h_count--;
} elsif ($symbol =~ /^[NOSP]$/ && $charge == 1) {
$h_count++;
} elsif ($symbol eq 'C' && $charge) {
$h_count--;
} elsif ($symbol eq 'B' && $charge == -1) {
$h_count++;
}
# some common radical situations
if ($radical == 1 or $radical == 3) {
# carbene, singlet or triplet
$h_count -= 2;
} elsif ($radical == 2) {
# radical (doublet)
$h_count--;
}
$h_count = 0 if $h_count < 0;
$h_count;
}
=item $atom->calc_implicit_hydrogens
Use heuristics to figure out how many implicit hydrogens should the atom have
to satisfy its normal "organic" valence. Returns the number of hydrogens but
does not affect the atom object.
=cut
sub calc_implicit_hydrogens {
my ($self) = @_;
$self->_calc_implicit_hydrogens(
$self->symbol, $self->explicit_valence,
$self->formal_charge, $self->formal_radical,
);
}
=item $atom->add_implicit_hydrogens
Similar to calc_implicit_hydrogens, but it also sets the number of implicit
hydrogens in the atom to the new calculated value. Equivalent to
$atom->implicit_hydrogens($atom->calc_implicit_hydrogens);
It returns the atom object.
=cut
sub add_implicit_hydrogens {
my ($self) = @_;
my $h_count = $self->calc_implicit_hydrogens;
$self->implicit_hydrogens($h_count);
}
=item $atom->aromatic($bool)
Set or get whether the atom is considered to be aromatic. This property may be
set arbitrarily, it doesn't imply any kind of "intelligent aromaticity
detection"! (For that, look at the L<Chemistry::Ring> module).
=cut
Chemistry::Obj::accessor('aromatic');
=item $atom->valence
Returns the sum of the bond orders of the bonds in which the atom participates,
including implicit hydrogens (which are assumed to have bond orders of one).
=cut
sub valence {
my ($self) = @_;
my $valence = 0;
$valence += $_->order for $self->bonds;
$valence += $self->hydrogens || 0;
$valence;
}
=item $atom->explicit_valence
Like C<valence>, but excluding implicit hydrogen atoms. To get the raw number
of bonds, without counting bond orders, call $atom->bonds in scalar context.
=cut
sub explicit_valence {
my ($self) = @_;
my $valence = 0;
$valence += $_->order for $self->bonds;
$valence;
}
# this method is for internal use only; called by $mol->add_bond
sub add_bond {
my $self = shift;
my $bond = shift;
my %seen;
#return if first { $_ eq $bond } @{$self->{bonds}};
for my $atom (@{$bond->{atoms}}){ #for each atom...
if ($atom ne $self) {
my $b = {to=>$atom, bond=>$bond};
weaken($b->{to});
weaken($b->{bond});
push @{$self->{bonds}}, $b;
}
}
}
# make sure the atom doesn't cause circular references
sub _weaken {
my $self = shift;
for my $b (@{$self->{bonds}}) {
weaken($b->{to});
weaken($b->{bond});
}
weaken($self->{parent});
}
# This method is private. Bonds should be deleted from the
# mol object. These methods should only be called by
# $bond->delete_atoms, which is called by $mol->delete_bond
sub delete_bond {
my ($self, $bond) = @_;
$self->{bonds} = [ grep { $_->{bond} ne $bond } @{$self->{bonds}} ];
}
=item $atom->delete
Calls $mol->delete_atom($atom) on the atom's parent molecule.
=cut
sub delete {
my ($self) = @_;
$self->{parent}->_delete_atom($self);
}
=item $atom->parent
Returns the atom's containing object (the molecule to which the atom belongs).
An atom can only have one parent.
=cut
sub parent {
my $self = shift;
if (@_) {
($self->{parent}) = @_;
weaken($self->{parent});
$self;
} else {
$self->{parent};
}
}
=item $atom->neighbors($from)
Return a list of neighbors. If an atom object $from is specified, it will be
excluded from the list (this is useful if an atom wants to know who its
neighbor's neighbors are, without counting itself).
=cut
sub neighbors {
my $self = shift;
my $from = shift;
my @ret = ();
for my $b (@{$self->{bonds}}) {
push @ret, $b->{to} unless $from && $b->{to} eq $from;
}
@ret;
}
=item $atom->bonds($from)
Return a list of bonds. If an atom object $from is specified, bonds to
that atom will be excluded from the list.
=cut
sub bonds {
my $self = shift;
my $from = shift;
my @ret = ();
for my $b (@{$self->{bonds}}) {
push @ret, $b->{bond} unless $from && $b->{to} eq $from;
}
@ret;
}
=item $atom->bonds_neighbors($from)
Return a list of hash references, representing the bonds and neighbors from the
atom. If an atom object $from is specified, it will be excluded from the list.
The elements of the hash are 'to', and atom reference, and 'bond', a bond
reference. For example,
for my $bn ($atom->bonds_neighbors) {
print "bond $bn->{bond} point to atom $bn->{to}\n";
}
=cut
sub bonds_neighbors {
my $self = shift;
my $from = shift;
my @ret = ();
for my $b (@{$self->{bonds}}) {
push @ret, {%$b} unless $from && $b->{to} eq $from;
}
@ret;
}
=item ($distance, $closest_atom) = $atom->distance($obj)
Returns the minimum distance to $obj, which can be an atom, a molecule, or a
vector. In scalar context it returns only the distance; in list context it
also returns the closest atom found. It can also be called as a function,
Chemistry::Atom::distance (which can be exported).
=cut
sub distance {
my $self = shift;
my $obj = shift;
my $min_length;
my $closest_atom = $obj;
if ($obj->isa('Chemistry::Atom')) {
my $v = $self->coords - $obj->coords;
$min_length = $v->length;
} elsif ($obj->isa('Math::VectorReal')) {
my $v = $self->coords - $obj;
$min_length = $v->length;
} elsif ($obj->isa('Chemistry::Mol')) {
my @atoms = $obj->atoms;
my $a = shift @atoms or return undef; # ensure there's at least 1 atom
$min_length = $self->distance($a);
$closest_atom = $a;
for $a (@atoms) {
my $l = $self->distance($a);
$min_length = $l, $closest_atom = $a if $l < $min_length;
}
} else {
croak "atom->distance() undefined for objects of type '", ref $obj,"'";
}
wantarray ? ($min_length, $closest_atom) : $min_length;
}
=item $atom->angle($atom2, $atom3)
Returns the angle in radians between the atoms involved. $atom2 is the atom in
the middle. Can also be called as Chemistry::Atom::angle($atom1, $atom2,
$atom3). This function can be exported. Note: if you override this method,
you may also need to override angle_deg or strange things may happen.
=cut
# $a2 is the one in the center
sub angle {
@_ == 3 or croak "Chemistry::Atom::angle requires three atoms!\n";
my @c;
for my $a (@_) { # extract coordinates
ref $a or croak "Chemistry::Atom::angle: $a is not an object";
push @c, $a->isa("Chemistry::Atom") ? $a->coords :
$a->isa("Math::VectorReal") ? $a :
croak "angle: $a is neither an atom nor a vector!\n";
}
my $v1 = $c[0] - $c[1];
my $v2 = $c[2] - $c[1];
my $l = ($v1->length * $v2->length) or return 0;
acos(($v1 . $v2) / $l);
}
=item $atom->angle_deg($atom2, $atom3)
Same as angle(), but returns the value in degrees. May be exported.
=cut
sub angle_deg {
rad2deg(angle(@_));
}
=item $atom->dihedral($atom2, $atom3, $atom4)
Returns the dihedral angle in radians between the atoms involved. Can also be
called as Chemistry::Atom::dihedral($atom1, $atom2, $atom3, $atom4). May be
exported. Note: if you override this method, you may also need to override
dihedral_deg and angle or strange things may happen.
=cut
sub dihedral {
@_ == 4 or croak "Chemistry::Atom::dihedral requires four atoms!\n";
my @c;
for my $a (@_) { # extract coordinates
push @c, $a->isa("Chemistry::Atom") ? $a->coords :
$a->isa("Math::VectorReal") ? $a :
croak "angle: $a is neither an atom nor a vector!\n";
}
my $v1 = $c[0] - $c[1];
my $v2 = $c[2] - $c[1];
my $v3 = $c[3] - $c[2];
my $x1 = $v1 x $v2;
my $x2 = $v3 x $v2;
my $abs_dih = angle($x1, O(), $x2);
$v1 . $x2 > 0 ? $abs_dih : -$abs_dih;
}
=item $atom->dihedral_deg($atom2, $atom3, $atom4)
Same as dihedral(), but returns the value in degrees. May be exported.
=cut
sub dihedral_deg {
rad2deg(dihedral(@_));
}
=item $atom->print
Convert the atom to a string representation (used for debugging).
=cut
sub print {
my $self = shift;
my ($indent) = @_;
no warnings;
$indent ||= 0;
my $bonds = join " ", map {$_->id} $self->bonds;
my $neighbors = join " ", map {$_->id} $self->neighbors;
my $coords = $self->{coords}->stringify(
'x3: %g
y3: %g
z3: %g'
);
my $ret = <<EOF;
$self->{id}:
symbol: $self->{symbol}
name : $self->{name}
$coords
formal_charge: $self->{formal_charge}
bonds: "$bonds"
neighbors: "$neighbors"
EOF
$ret .= " attr:\n";
$ret .= $self->print_attr($indent+2);
$ret =~ s/^/" "x$indent/gem;
$ret;
}
=item my $info = $atom->sprintf($format)
Format interesting atomic information in a concise way, as specified by
a printf-like format.
%s - symbol
%Z - atomic number
%n - name
%q - formal charge
%h - implicit hydrogen count
%v - valence
%i - id
%8.3m - mass, formatted as %8.3f with core sprintf
%8.3x - x coordinate, formatted as %8.3f with core sprintf
%8.3y - y coordinate, formatted as %8.3f with core sprintf
%8.3z - z coordinate, formatted as %8.3f with core sprintf
%% - %
=cut
sub sprintf {
my ($atom, $format) = @_;
no warnings 'uninitialized'; # don't care if some properties are undefined
$format ||= "%f";
$format =~ s/%%/\\%/g; # escape %% with a \
$format =~ s/(?<!\\)%q/$atom->formal_charge || 0/eg; # %q
$format =~ s/(?<!\\)%s/$atom->symbol/eg; # %s
$format =~ s/(?<!\\)%Z/$atom->Z/eg; # %Z
$format =~ s/(?<!\\)%n/$atom->name/eg; # %n
$format =~ s/(?<!\\)%h/$atom->hydrogens/eg; # %h
$format =~ s/(?<!\\)%v/$atom->valence/eg; # %v
$format =~ s/(?<!\\)%(\d*\.?\d*)m/
$1 ? sprintf "%$1f", $atom->mass : $atom->mass/eg; # %m
$format =~ s/(?<!\\)%(\d*\.?\d*)x/
$1 ? sprintf "%$1f", $atom->x3 : $atom->x3/eg; # %x
$format =~ s/(?<!\\)%(\d*\.?\d*)y/
$1 ? sprintf "%$1f", $atom->y3 : $atom->y3/eg; # %y
$format =~ s/(?<!\\)%(\d*\.?\d*)z/
$1 ? sprintf "%$1f", $atom->z3 : $atom->z3/eg; # %z
$format =~ s/(?<!\\)%i/$atom->id/eg; # %i
$format =~ s/\\(.)/$1/g; # other \ escapes
$format;
}
=item $atom->printf($format)
Same as $atom->sprintf, but prints to standard output automatically. Used
for quick and dirty atomic information dumping.
=cut
sub printf {
my ($atom, $format) = @_;
print $atom->sprintf($format);
}
1;
=back
=head1 VERSION
0.37
=head1 SEE ALSO
L<Chemistry::Mol>, L<Chemistry::Bond>,
L<Math::VectorReal>, L<Chemistry::Tutorial>,
L<Chemistry::InternalCoords>
The PerlMol website L<http://www.perlmol.org/>
=head1 AUTHOR
Ivan Tubert-Brohman E<lt>itub@cpan.orgE<gt>
=head1 COPYRIGHT
Copyright (c) 2005 Ivan Tubert-Brohman. All rights reserved. This program is
free software; you can redistribute it and/or modify it under the same terms as
Perl itself.
=cut