Provided by: libmath-planepath-perl_122-1_all 
NAME
Math::PlanePath::ImaginaryBase -- replications in four directions
SYNOPSIS
use Math::PlanePath::ImaginaryBase;
my $path = Math::PlanePath::ImaginaryBase->new (radix => 4);
my ($x, $y) = $path->n_to_xy (123);
DESCRIPTION
This is a simple pattern arising from complex numbers expressed in a base i*sqrt(2) or
other i*sqrt(r) base. Or equivalently by negabinary encoded X,Y digits interleaved. The
default radix=2 is
38 39 34 35 54 55 50 51 5
36 37 32 33 52 53 48 49 4
46 47 42 43 62 63 58 59 3
44 45 40 41 60 61 56 57 2
6 7 2 3 22 23 18 19 1
4 5 0 1 20 21 16 17 <- Y=0
14 15 10 11 30 31 26 27 -1
12 13 8 9 28 29 24 25 -2
^
-2 -1 X=0 1 2 3 4 5
The pattern can be seen by dividing into blocks as follows,
+---------------------------------------+
| 38 39 34 35 54 55 50 51 |
| |
| 36 37 32 33 52 53 48 49 |
| |
| 46 47 42 43 62 63 58 59 |
| |
| 44 45 40 41 60 61 56 57 |
+---------+---------+-------------------+
| 6 7 | 2 3 | 22 23 18 19 |
| +----+----+ |
| 4 5 | 0 | 1 | 20 21 16 17 |
+---------+----+----+ |
| 14 15 10 11 | 30 31 26 27 |
| | |
| 12 13 8 9 | 28 29 24 25 |
+-------------------+-------------------+
After N=0 at the origin, N=1 replicates that single point to the right. Then that pair
repeats above as N=2 and N=3. Then that 2x2 block repeats to the left as N=4 to N=7, then
4x2 repeated below as N=8 to N=16. Then 4x4 to the right as N=16 to N=31, etc. Each
repeat is 90 degrees further around. The relative layout and orientation of a sub-part is
unchanged when replicated.
Complex Base
This pattern arises from representing a complex number in "base" i*sqrt(r). For an
integer X,Y,
b = i*sqrt(r)
a[i] = 0 to r-1 digits
X+Y*i*sqrt(r) = a[k]*b^k + ... + a[2]*b^2 + a[1]*b + a[0]
and N is the a[i] digits in base r
N = a[k]*r^k + ... + a[2]*r^2 + a[1]*r + a[0]
The factor sqrt(r) makes the generated Y an integer. For actual use as a number base that
factor can be omitted and instead fractional digits a[-1]*r^-1 etc used to reach smaller Y
values, as for example in Knuth's "quater-imaginary" system of base 2*i, being i*sqrt(4),
with digits 0,1,2,3. (Knuth Seminumerical Algorithms section 4.1 and CACM 1960
pp245-247.)
The powers of i in the base give the replication direction, so i^0=1 right, i^1=i up,
i^2=-1 right, i^3=-i down, etc. The power of sqrt(r) then spreads the replication in the
respective direction. It takes two steps to repeat horizontally and sqrt(r)^2=r hence the
doubling of 1x1 to the right, 2x2 to the left, 4x4 to the right, etc, and similarly
vertically.
Negabinary
The way blocks repeat horizontally first to the right and then to the left is per the
negabinary system base b=-2.
X = x[k]*(-2)^k + ... + x[2]*(-2)^2 + x[1]*(-2) + x[0]
The effect is to represent any positive or negative X by a positive integer index NX.
X, negabinary: ... -1 -2 0 1 2 3 4 5 ...
index NX: 2 3 0 1 6 7 4 5
Notice how the 0 point replicates to the right as 1 and then that pair 0,1 replicates to
the left as 2,3. Then the block 2,3,0,1 repeats to the right as 6,7,4,5 which the same
order with 4 added to each. Then the resulting block of eight repeats to the left
similarly, in the same order with 8 added to each.
The "ImaginaryBase" takes the indexes NX and NY of these negabinary forms and forms N by
interleaving the digits (bits) of NX and NY. That interleaving is in the style of the
"ZOrderCurve".
zX,zY = ZOrderCurve n_to_xy(N)
X = to_negabinary(zX)
Y = to_negabinary(zY)
X,Y equals ImaginaryBase n_to_xy(N)
The "ZOrderCurve" replicates blocks alternately right and up, whereas for "ImaginaryBase"
here it's right,up,left,down repeating.
Radix
The "radix" parameter controls the radix used to break N into X,Y. For example radix 3
replicates to make 3x1, 3x3, 9x3, 9x9, etc blocks. The replications are radix-1=2 copies
of the preceding level at each stage,
radix => 3
+------------------------+-----------+
| 24 25 26 15 16 17 | 6 7 8 | 2
| | |
| 21 22 23 12 13 14 | 3 4 5 | 1
| +-----------+
| 18 19 20 9 10 11 | 0 1 2 | <- Y=0
+------------------------+-----------+
| 51 52 53 42 43 44 33 34 35 | -1
| |
| 48 49 50 39 40 41 30 31 32 | -2
| |
| 45 46 47 36 37 38 27 28 29 | -3
| |
| 78 79 80 69 70 71 60 61 62 | -4
| |
| 75 76 77 66 67 68 57 58 59 | -5
| |
| 72 73 74 63 64 65 54 55 56 | -6
+------------------------------------+
^
-6 -5 -4 -3 -2 -1 X=0 1 2
X,Y are "negaternary" in this case, and similar negaradix base=-radix for higher values.
FUNCTIONS
See "FUNCTIONS" in Math::PlanePath for behaviour common to all path classes.
"$path = Math::PlanePath::ImaginaryBase->new ()"
"$path = Math::PlanePath::ImaginaryBase->new (radix => $r)"
Create and return a new path object.
"($x,$y) = $path->n_to_xy ($n)"
Return the X,Y coordinates of point number $n on the path. Points begin at 0 and if
"$n < 0" then the return is an empty list.
"($n_lo, $n_hi) = $path->rect_to_n_range ($x1,$y1, $x2,$y2)"
The returned range is exact, meaning $n_lo and $n_hi are the smallest and biggest in
the rectangle.
Level Methods
"($n_lo, $n_hi) = $path->level_to_n_range($level)"
Return "(0, $radix**$level - 1)".
FORMULAS
Rectangle to N Range
The X and Y ranges can be treated separately and then interleaved,
NXmin,NXmax = negaradix range to cover x1..x2
NYmin,NYmax = negaradix range to cover y1..y2
Nmin = interleave digits NXmin, NYmin
Nmax = interleave digits NXmax, NYmax
If the NX,NY ranges are exact then the resulting Nmin,Nmax range is exact.
An exact negaradix range can be calculated by digits high to low by considering the range
taken by the negaradix form. For example two negaternary digits,
N digit 2 1 0
+---------+---------+---------+
N index | 6 7 8 | 3 4 5 | 0 1 2 |
+---------+---------+---------+
X negaternary -6 -5 -4 -3 -2 -1 0 1 2
^
base
Taking the base=-90909...90 which is the lowest taken (where 9 is the radix digit R-1),
then the next digit of N is the position from X-base, taken alternately reverse 2,1,0 as
shown here or forward 0,1,2.
OEIS
Entries in Sloane's Online Encyclopedia of Integer Sequences related to this path include,
<http://oeis.org/A057300> (etc)
radix=2
A057300 permutation N at transpose Y,X (swap bit pairs)
radix=3
A163327 permutation N at transpose Y,X (swap trit pairs)
radix=4
A126006 permutation N at transpose Y,X (swap digit pairs)
radix=16
A217558 permutation N at transpose Y,X (swap digit pairs)
SEE ALSO
Math::PlanePath, Math::PlanePath::ImaginaryHalf, Math::PlanePath::CubicBase,
Math::PlanePath::ZOrderCurve
HOME PAGE
<http://user42.tuxfamily.org/math-planepath/index.html>
LICENSE
Copyright 2011, 2012, 2013, 2014, 2015 Kevin Ryde
Math-PlanePath 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-PlanePath 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-
PlanePath. If not, see <http://www.gnu.org/licenses/>.