# Copyright 2011, 2012, 2013, 2014 Kevin Ryde
# This file is part of Math-NumSeq.
#
# Math-NumSeq 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 3, or (at your option) any later
# version.
#
# Math-NumSeq 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 Math-NumSeq. If not, see <http://www.gnu.org/licenses/>.
# Fractal turn sequence:
# "Infinite streams", Jorg Endrullis, Clemens Grabmayer, Dimitri Hendriks,
# Jan Willem Klop, www.phil.uu.nl/~clemens/linkedfiles/NVTI2009.pdf
package Math::NumSeq::MephistoWaltz;
use 5.004;
use strict;
use vars '$VERSION', '@ISA';
$VERSION = 70;
use Math::NumSeq;
@ISA = ('Math::NumSeq');
*_is_infinite = \&Math::NumSeq::_is_infinite;
# uncomment this to run the ### lines
#use Smart::Comments;
# use constant name => Math::NumSeq::__('Mephisto Waltz');
use constant description => Math::NumSeq::__('Mephisto waltz sequence.');
use constant i_start => 0;
use constant values_min => 0;
use constant values_max => 1;
use constant characteristic_integer => 1;
# cf A189658 - positions of 0
# A189659 - positions of 1
# A189660 - cumulative 0/1
# A156595 - xor diffs, OFFSET=0 so a(n) = m(n) xor m(n+1)
#
use constant oeis_anum => 'A064990'; # mephisto waltz 0/1 values
sub rewind {
my ($self) = @_;
$self->{'i'} = $self->i_start;
$self->{'value'} = 1;
$self->{'low'} = -1;
$self->{'digits'} = [];
}
my @table = (0,0,1, 0,0,1, 1,1,0,
0,0,1, 0,0,1, 1,1,0,
1,1,0, 1,1,0, 0,0,1);
my @delta = (map {$table[$_]^$table[($_+26)%27]} 0 .. $#table);
sub next {
my ($self) = @_;
### MephistoWaltz next(): $self->{'i'}
### at: "low=$self->{'low'} value=$self->{'value'}"
my $low;
if (($low = ++$self->{'low'}) >= 27) {
$low = $self->{'low'} = 0;
my $i = 0;
for (;;) {
my $digit = ++$self->{'digits'}->[$i];
### carry to digit: $digit
if ($digit >= 27) {
$self->{'digits'}->[$i++] = 0;
$self->{'value'} ^= 1; # three 2s have become 0s
} else {
$self->{'value'} ^= $delta[$digit];
last;
}
}
}
### apply: "low=$low delta=$delta[$low]"
return ($self->{'i'}++,
($self->{'value'} ^= $delta[$low]));
}
sub ith {
my ($self, $i) = @_;
### ith(): $i
if (_is_infinite($i)) {
return $i;
}
my $ret = 0;
while ($i) {
$ret ^= $table[$i % 27];
$i = int($i/27);
}
return $ret;
}
sub pred {
my ($self, $value) = @_;
return ($value == 0 || $value == 1);
}
1;
__END__
=for stopwords Ryde Math-NumSeq Mephisto MephistoWaltz
=head1 NAME
Math::NumSeq::MephistoWaltz -- Mephisto waltz sequence
=head1 SYNOPSIS
use Math::NumSeq::MephistoWaltz;
my $seq = Math::NumSeq::MephistoWaltz->new;
my ($i, $value) = $seq->next;
=head1 DESCRIPTION
The Mephisto waltz sequence, being the mod 2 count of ternary digit 2s in i.
0,0,1, 0,0,1, 1,1,0, ...
starting i=0
i=0 has no 2s so value=0, and likewise i=1 value=0. Then i=2 has one 2 so
value=1.
The sequence can also be expressed as starting with 0 and repeatedly
expanding
0 -> 0,0,1
1 -> 1,1,0
So
0
0,0,1
0,0,1, 0,0,1, 1,1,0,
0,0,1, 0,0,1, 1,1,0, 0,0,1, 0,0,1, 1,1,0, 1,1,0, 1,1,0, 0,0,1
| original | | copy | | inverse |
+-----------------+ +-----------------+ +-----------------+
The effect of the expansion is keep the first third the same, append a copy
of it, and append an inverse of it 0E<lt>-E<gt>1.
=head1 FUNCTIONS
See L<Math::NumSeq/FUNCTIONS> for behaviour common to all sequence classes.
=over 4
=item C<$seq = Math::NumSeq::MephistoWaltz-E<gt>new ()>
Create and return a new sequence object.
=back
=head2 Random Access
=over
=item C<$value = $seq-E<gt>ith($i)>
Return the C<$i>'th MephistoWaltz value, being the count mod 2 of the
ternary digit 2s in C<$i>.
=item C<$bool = $seq-E<gt>pred($value)>
Return true if C<$value> occurs in the sequence, which simply means 0 or 1.
=back
=head1 FORMULAS
The calculation can be made in a power-of-3 base like 9, 27, 81, etc instead
of just 3. For example in base 9 digits 2, 5, 6, 7 have a one (mod 2)
ternary 2. These base 9 digits correspond to the 1s in the initial sequence
0,0,1, 0,0,1, 1,1,0 shown above.
=head1 SEE ALSO
L<Math::NumSeq>,
L<Math::NumSeq::DigitSumModulo>
=head1 HOME PAGE
L<http://user42.tuxfamily.org/math-numseq/index.html>
=head1 LICENSE
Copyright 2011, 2012, 2013, 2014 Kevin Ryde
Math-NumSeq 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 3, or (at your option) any later
version.
Math-NumSeq 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
Math-NumSeq. If not, see <http://www.gnu.org/licenses/>.
=cut