Provided by: libmath-planepath-perl_129-1_all 
NAME
Math::NumSeq::PlanePathDelta -- sequence of changes and directions of PlanePath
coordinates
SYNOPSIS
use Math::NumSeq::PlanePathDelta;
my $seq = Math::NumSeq::PlanePathDelta->new
(planepath => 'SquareSpiral',
delta_type => 'dX');
my ($i, $value) = $seq->next;
DESCRIPTION
This is a tie-in to present coordinate changes and directions from a "Math::PlanePath"
module in the form of a NumSeq sequence.
The "delta_type" choices are
"dX" change in X coordinate
"dY" change in Y coordinate
"AbsdX" abs(dX)
"AbsdY" abs(dY)
"dSum" change in X+Y, equals dX+dY
"dSumAbs" change in abs(X)+abs(Y)
"dDiffXY" change in X-Y, equals dX-dY
"dDiffYX" change in Y-X, equals dY-dX
"dAbsDiff" change in abs(X-Y)
"dRadius" change in Radius sqrt(X^2+Y^2)
"dRSquared" change in RSquared X^2+Y^2
"Dir4" direction 0=East, 1=North, 2=West, 3=South
"TDir6" triangular 0=E, 1=NE, 2=NW, 3=W, 4=SW, 5=SE
In each case the value at i is per "$path->n_to_dxdy($i)", being the change from N=i to
N=i+1, or from N=i to N=i+arms for paths with multiple "arms" (thus following the arm). i
values start from the usual "$path->n_start()".
AbsdX,AbsdY
If a path always steps NSEW by 1 then AbsdX and AbsdY behave as a boolean indicating
horizontal or vertical step,
NSEW steps by 1 gives
AbsdX = 0 vertical AbsdY = 0 horizontal
1 horizontal 1 vertical
If a path includes diagonal steps by 1 then those diagonals are a non-zero delta, so the
indication is then
NSEW and diagonals steps by 1 gives
AbsdX = 0 vertical AbsdY = 0 horizontal
1 non-vertical 1 non-horizontal
ie. horiz or diag ie. vert or diag
dSum
"dSum" is the change in X+Y and is also simply dX+dY since
dSum = (Xnext+Ynext) - (X+Y)
= (Xnext-X) + (Ynext-Y)
= dX + dY
The sum X+Y counts anti-diagonals, as described in Math::NumSeq::PlanePathCoord. dSum is
therefore a move between diagonals, or 0 if a step stays within the same diagonal.
\
\ ^ dSum > 0 dSum = step dist to North-East
\/
/\
dSum < 0 v \
\
dSumAbs
"dSumAbs" is the change in the abs(X)+abs(Y) sum,
dSumAbs = (abs(Xnext)+abs(Ynext)) - (abs(X)+abs(Y))
As described in "SumAbs" in Math::NumSeq::PlanePathCoord, SumAbs is a "Manhattan" or
"taxi-cab" distance from the origin, or equivalently a move between diamond-shaped rings.
For example "DiamondSpiral" follows a diamond shape ring around and so has dSumAbs=0 until
stepping out to each next diamond with dSumAbs=1.
A path might make a big X,Y jump which is only a small change in SumAbs. For example
"PyramidRows" in its default step=2 from the end of one row to the start of the next has
dSumAbs=2.
dDiffXY and dDiffYX
"dDiffXY" is the change in DiffXY = X-Y, which is also simply dX-dY since
dDiffXY = (Xnext-Ynext) - (X-Y)
= (Xnext-X) - (Ynext-Y)
= dX - dY
The difference X-Y counts diagonals downwards to the south-east as described in "Sum and
Diff" in Math::NumSeq::PlanePathCoord. dDiffXY is therefore movement between those
diagonals, or 0 if a step stays within the same diagonal.
dDiffXY < 0 /
\ / dDiffXY = step dist to South-East
\/
/\
/ v
/ dDiffXY > 0
"dDiffYX" is the negative of dDiffXY. Whether X-Y or Y-X is desired depends on which way
you want to measure diagonals, or which way around to have the sign for the changes.
dDiffYX is based on Y-X and so counts diagonals upwards to the North-West.
dAbsDiff
"dAbsDiff" is the change in AbsDiff = abs(X-Y). AbsDiff can be interpreted geometrically
as distance from the leading diagonal, as described in "AbsDiff" in
Math::NumSeq::PlanePathCoord. dAbsDiff is therefore movement closer to or further away
from that leading diagonal, measuring perpendicular to it.
/ X=Y line
/
/ ^
/ \
/ * dAbsDiff move towards or away from X=Y line
|/ \
--o-- v
/|
/
When an X,Y jumps from one side of the diagonal to the other dAbsDiff is still the change
in distance from the diagonal. So for example if X,Y is followed by the mirror point Y,X
then dAbsDiff=0. That sort of thing happens for example in the "Diagonals" path when
jumping from the end of one run to the start of the next. In the "Diagonals" case it's a
move just 1 further away from the X=Y centre line even though it's a big jump in overall
distance.
dRadius, dRSquared
"dRadius" and "dRSquared" are the change in the Radius and RSquared as described in
"Radius and RSquared" in Math::NumSeq::PlanePathCoord.
dRadius = next_Radius - Radius
dRSquared = next_RSquared - RSquared
dRadius can be interpreted geometrically as movement towards (negative values) or away
from (positive values) the origin, ignoring direction.
Notice that dRadius is not sqrt(dRSquared), since sqrt(n^2-t^2) != n-t unless n or t is
zero. Here would mean a step either going to or coming from the origin 0,0.
Dir4
"Dir4" is the curve step direction as an angle in the range 0 <= Dir4 < 4. The cardinal
directions E,N,W,S are 0,1,2,3. Angles in between are a fraction.
Dir4 = atan2(dY,dX) scaled as range 0 <= Dir4 < 4
1.5 1 0.5
\ | /
\|/
2 ----o---- 0
/|\
/ | \
2.5 3 3.5
If a row such as Y=-1,X>0 just below the X axis is visited then the Dir4 approaches 4,
without ever reaching it. The "$seq->value_maximum()" is 4 in this case, as a supremum.
TDir6
"TDir6" is the curve step direction 0 <= TDir6 < 6 taken in the triangular style of
"Triangular Lattice" in Math::PlanePath. So dX=1,dY=1 is taken to be 60 degrees which is
TDir6=1.
2 1.5 1 TDir6
\ | /
\|/
3 ---o--- 0
/|\
/ | \
4 4.5 5
Angles in between the six cardinal directions are fractions. North is 1.5 and South is
4.5.
The direction angle is calculated as if dY was scaled by a factor sqrt(3) to make the
lattice into equilateral triangles, or equivalently as a circle stretched vertically by
sqrt(3) to become an ellipse.
TDir6 = atan2(dY*sqrt(3), dX) in range 0 <= TDir6 < 6
Notice that angles on the axes dX=0 or dY=0 are not changed by the sqrt(3) factor. So
TDir6 has ENWS 0, 1.5, 3, 4.5 which is steps of 1.5. Verticals North and South normally
don't occur in the triangular lattice paths which go by unit steps, but TDir6 can be
applied on any path.
The sqrt(3) factor increases angles in the middle of the quadrants. For example dX=1,dY=1
becomes TDir6=1 whereas a plain angle would be only 45/360*6=0.75 in the same 0 to 6
scale. The sqrt(3) is a continuous scaling, so a plain angle and a TDir6 are a one-to-one
mapping. As the direction progresses through the quadrant TDir6 grows first faster and
then slower than the plain angle.
FUNCTIONS
See "FUNCTIONS" in Math::NumSeq for behaviour common to all sequence classes.
"$seq = Math::NumSeq::PlanePathDelta->new (key=>value,...)"
Create and return a new sequence object. The options are
planepath string, name of a PlanePath module
planepath_object PlanePath object
delta_type string, as described above
"planepath" can be either the module part such as "SquareSpiral" or a full class name
"Math::PlanePath::SquareSpiral".
"$value = $seq->ith($i)"
Return the change at N=$i in the PlanePath.
"$i = $seq->i_start()"
Return the first index $i in the sequence. This is the position "$seq->rewind()"
returns to.
This is "$path->n_start()" from the PlanePath.
BUGS
Some path sequences don't have "oeis_anum()" and are not available through
Math::NumSeq::OEIS entry due to the path "n_start()" not matching the OEIS "offset".
Paths with an "n_start" parameter have suitable adjustments applied, but those without are
omitted from the Math::NumSeq::OEIS mechanism presently.
SEE ALSO
Math::NumSeq, Math::NumSeq::PlanePathCoord, Math::NumSeq::PlanePathTurn,
Math::NumSeq::PlanePathN
Math::PlanePath
HOME PAGE
<http://user42.tuxfamily.org/math-planepath/index.html>
LICENSE
Copyright 2011, 2012, 2013, 2014, 2015, 2016, 2017, 2018, 2019, 2020, 2021 Kevin Ryde
This file is part of Math-PlanePath.
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/>.