Masteries · Jason GlowneyArithmoí Book 1

Masteries

1.4.5 Number Forms, Odd and Even Partition Geometry, and Minimal Elements

On the way to find­ing the number of per­mu­ta­tion el­e­ments ∈D3ℂΔ\in D_{3\mathbb{C}}^{\Delta}, we made use of num­bers that were de­scribed as cone num­bers and axis num­bers. De­vel­op­ing an in­tu­ition for these num­bers comes by ex­pand­ing beyond a simple al­ge­bra­ic de­scrip­tion, to one that en­com­pass­es their geom­e­try. Our spa­tial abil­i­ty to con­sid­er higher-di­men­sion­al number forms may be hin­dered when trying to vi­su­al­ize them, but we can con­sid­er pro­ject­ing our equi­lat­er­al tri­an­gle ∈ℂ3\in \mathbb{C}^{3} onto a disc ∈ℂ1\in \mathbb{C}^{1} space. The con­sid­er­a­tions of arc length and areas on the com­plex unit circle, along with their spher­i­cal analogs, reveal that some num­bers and their area/vol­umes are sub­sets of other ones. For the real in­te­gers and ra­tio­nal num­bers, we are aware of the con­cept of even and odd num­bers, for which, the fol­low­ing hold:

even+even=even,even + even = even,
even+odd=odd,even + odd = odd,
odd+odd=even,odd + odd = even,
odd×odd=odd,odd \times odd = odd,
even×even=even,even \times even = even,
odd×even=even.odd \times even = even.

The ex­am­ple con­sid­ered is a de­fined group AA, which rep­re­sents the even nat­ur­al num­bers, with op­er­a­tions of ad­di­tion and mul­ti­pli­ca­tion. The values of the nat­ur­al num­bers re­sult­ing from these op­er­a­tions will remain even and con­sis­tent with the even sub­group of the nat­ur­al num­bers A⊂ℕA\subset \mathbb{N}. Adding an odd number to any el­e­ment aa, in the AA sub­group, gives us an odd-valued nat­ur­al number ⊂ℕ\subset \mathbb{N}. If we choose the odd nat­ur­al number 1⊂ℕ1 \subset \mathbb{N}, then apply the ad­di­tion op­er­a­tion +1+ 1 to every el­e­ment ∈A\in A, the result will be the whole group of nat­ur­al num­bers

1+a: ∀a∈A→ℕ.\begin{array}{r} 1 + a:\ \forall a \in A\rightarrow \mathbb{N}. \end{array}
(1.4.88)

If we were to choose an odd nat­ur­al number such as 7,7,we would be miss­ing some of the odd nat­ur­al num­bers in the lower valued bound of the set, seen as fol­lows

{7,(a1+7),(a2+7),(a3+7),…}∪an={2,4,6,7,8,9,10,11,12+…},\begin{array}{r} \left\{ 7,{(a}_{1} + 7 \right),\left( a_{2} + 7 \right),\left( a_{3} + 7 \right),\ldots\} \cup a_{n} = \{ 2,4,6,7,8,9,10,11,12 + \ldots\}, \end{array}
(1.4.89)

for ana_{n}, the set of even nat­ur­al num­bers. In the above ex­pres­sion, we are miss­ing the odd nat­ur­al num­bers from 11 to 5, given that the first odd nat­ur­al number was chosen to be 77. As the number 11 is re­quired to com­plete the set of nat­ur­al num­bers, we define this to be the min­i­mal el­e­ment of the set, since there is no nat­ur­al number in the set that is small­er than it. The de­f­i­n­i­tion of the min­i­mal el­e­ment can also be con­sid­ered for the groups we have been study­ing. We can start by ap­ply­ing this con­cept to spheres, and we will even­tu­al­ly find the con­cept holds for the other dis­cussed matrix group conic sec­tions. This is elu­ci­dat­ed by ex­pand­ing from the simple nat­ur­al num­bers to the com­plex num­bers and their rep­re­sen­ta­tion as ex­po­nen­tials in higher di­men­sions.

To start, we con­sid­er the in­fi­nite set of com­plex num­bers on the unit circle using −1,- 1,raised to a vari­able power nq\frac{n}{q}, as (−1)(nq)( - 1)^{\left( \frac{n}{q} \right)}, for n∈ℤn\in \mathbb{Z}, q∈ℤ≥0q \in \mathbb{Z}_{\geq 0}, where the number zero is in­clud­ed for nn and qq. For n=1n = 1, the number (−1)(1q)( - 1)^{\left( \frac{1}{q} \right)} is the ar­clength in ra­di­ans from the pos­i­tive real-axis, fit­ting the de­f­i­n­i­tion of the pri­ma­ry min­i­mal el­e­ment. The number 2q2q is the total number of el­e­ments in the ar­clength par­ti­tion set on the in­ter­val [0,2iπ).\lbrack 0,2i\pi).We define the number 11, as

1=(−1)0,\begin{array}{r} 1 = ( - 1)^{0}, \end{array}
(1.4.90)

for n=0∧q∈ℤ≥0n = 0 \land q \in \mathbb{Z}_{\geq 0}, sig­ni­fy­ing that the total number of el­e­ments in the par­ti­tioned set is zero, defin­ing the non-par­ti­tioned in­ter­val. Ex­press­ing com­plex num­bers on the unit circle up to a pri­ma­ry min­i­mal el­e­ment (−1)(14)( - 1)^{\left( \frac{1}{4} \right)}, com­pris­es a set of min­i­mal pri­ma­ry el­e­ments {(−1)0,(−1)(11),(−1)(12),(−1)(13),(−1)(14)}\left\{ ( - 1)^{0},( - 1)^{\left( \frac{1}{1} \right)},( - 1)^{\left( \frac{1}{2} \right)},( - 1)^{\left( \frac{1}{3} \right)},( - 1)^{\left( \frac{1}{4} \right)} \right\}, for which the full sets are the fol­low­ing:

{(−1)0}={e0},{\{( - 1)}^{0}\} = \left\{ e^{0} \right\},
{(−1)01,(−1)11}={ei0,eiπ},{\{( - 1)}^{\frac{0}{1}},( - 1)^{\frac{1}{1}}\} = \left\{ e^{i0},e^{i\pi} \right\},
{(−1)02,(−1)12,(−1)22,(−1)32}={ei0,eiπ2,eiπ,ei3π2},{\{( - 1)}^{\frac{0}{2}},( - 1)^{\frac{1}{2}},( - 1)^{\frac{2}{2}},( - 1)^{\frac{3}{2}}\} = \left\{ e^{i0},{e^{\frac{i\pi}{2}},e}^{i\pi},e^{\frac{i3\pi}{2}} \right\},
{(−1)03,(−1)13,(−1)23,(−1)33,(−1)43,(−1)53}={ei0,eiπ3,ei2π3,eiπ,ei4π3,ei5π3},{\{( - 1)}^{\frac{0}{3}},( - 1)^{\frac{1}{3}},( - 1)^{\frac{2}{3}},( - 1)^{\frac{3}{3}}{,( - 1)}^{\frac{4}{3}},( - 1)^{\frac{5}{3}}\} = \left\{ e^{i0},{e^{\frac{i\pi}{3}},e}^{\frac{i2\pi}{3}},e^{i\pi},{e^{\frac{i4\pi}{3}},e}^{\frac{i5\pi}{3}} \right\},
{(−1)04,(−1)14,(−1)24,(−1)34,(−1)44,(−1)54,(−1)64,(−1)74}={ei0,eiπ4,eiπ2,ei3π4eiπ,ei5π4,ei3π2,ei7π4}.(1.4.91){\{( - 1)}^{\frac{0}{4}},( - 1)^{\frac{1}{4}},( - 1)^{\frac{2}{4}},( - 1)^{\frac{3}{4}},( - 1)^{\frac{4}{4}},( - 1)^{\frac{5}{4}},( - 1)^{\frac{6}{4}},( - 1)^{\frac{7}{4}}\} = \left\{ e^{i0},e^{\frac{i\pi}{4}},{e^{\frac{i\pi}{2}},e^{\frac{i3\pi}{4}}e}^{i\pi},e^{\frac{i5\pi}{4}},e^{\frac{i3\pi}{2}},e^{\frac{i7\pi}{4}} \right\}.(1.4.91)

When con­sid­er­ing the unit circle for odd-valued el­e­ments for the ra­tio­nal ex­po­nent nq\frac{n}{q} and the sets above, the powers of these el­e­ments will land on every member in the set when suc­ces­sive­ly it­er­at­ed. An ex­am­ple: for modulo 2π2\pi, the number (−1)(34)( - 1)^{\left( \frac{3}{4} \right)} lands on every el­e­ment in the pri­ma­ry min­i­mal el­e­ment set (−1)(14)( - 1)^{\left( \frac{1}{4} \right)}, seen by ex­pand­ing its se­quence

{((−1)34)m[0,7]}={(−1)0,(−1)34,(−1)64,(−1)94,(−1)124,(−1)154,(−1)184,(−1)214}\left\{ \left( ( - 1)^{\frac{3}{4}} \right)^{m\lbrack 0,7\rbrack} \right\} = \left\{ ( - 1)^{0},( - 1)^{\frac{3}{4}},( - 1)^{\frac{6}{4}},( - 1)^{\frac{9}{4}},( - 1)^{\frac{12}{4}},( - 1)^{\frac{15}{4}},( - 1)^{\frac{18}{4}},( - 1)^{\frac{21}{4}} \right\}
→{((−1)34)m(m=[0,7]:m∈ℤ+,mod 2π)}={ei0,eiπ4,eiπ2,ei3π4eiπ,ei5π4,ei3π2,ei7π4}.\begin{array}{r} \rightarrow \left\{ \left( ( - 1)^{\frac{3}{4}} \right)^{m}\left( m = \lbrack 0,7\rbrack:m \in \mathbb{Z}^{+},mod\ 2\pi \right) \right\} = \left\{ e^{i0},e^{\frac{i\pi}{4}},{e^{\frac{i\pi}{2}},e^{\frac{i3\pi}{4}}e}^{i\pi},e^{\frac{i5\pi}{4}},e^{\frac{i3\pi}{2}},e^{\frac{i7\pi}{4}} \right\}. \end{array}
(1.4.92)

For geo­met­ric spaces like the hy­per­bo­la, this would not hold as the hy­per­bo­la is open and suc­ces­sive el­e­ments in the set would con­tin­ue to extend in­def­i­nite­ly out in the geom­e­try, seen by using the anal­o­gous ex­am­ple in the hy­per­bol­ic sense

{(e3π4)m(m=[0,7]:m∈ℤ+)}={e0,e3π4,e6π4,e9π4e3π,e15π4,e18π4,e21π4}.\begin{array}{r} \left\{ \left( e^{\frac{3\pi}{4}} \right)^{m}\left( m = \lbrack 0,7\rbrack:m \in \mathbb{Z}^{+} \right) \right\} = \left\{ e^{0},e^{\frac{3\pi}{4}},{e^{\frac{6\pi}{4}},e^{\frac{9\pi}{4}}e}^{3\pi},e^{\frac{15\pi}{4}},e^{\frac{18\pi}{4}},e^{\frac{21\pi}{4}} \right\}. \end{array}
(1.4.93)

So, in the case of suc­ces­sive ro­ta­tions on a com­plex sphere, where we want to track non-modulo powers, our pri­ma­ry min­i­mal el­e­ment is like the case of our nat­ur­al num­bers for 11, and is the only el­e­ment that when mul­ti­plied by itself will yield every el­e­ment in the set. This should sound con­sis­tent with a cyclic group, at least for the two-di­men­sion­al case on the com­plex unit circle. If our goal is to find a sym­met­ric group, we need to think along the lines of taking ad­van­tage of min­i­mal el­e­ments to arrive at all the el­e­ments in the group. Min­i­mal el­e­ments, and any con­gru­ent modulo 2π2\pi el­e­ments for the ex­po­nent nq\frac{n}{q} equal­ing an odd ra­tio­nal, is anal­o­gous to the odd num­bers from the case of the nat­ur­al num­bers with the de­fined mul­ti­pli­ca­tion op­er­a­tion, where ex­po­nents will add and the fol­low­ing hold,

aevenbeven =abeven+even=abeven,a^{even}b^{even\ } = ab^{even + even} = ab^{even},
aoddbeven =abodd+even=abodd,a^{odd}b^{even\ } = ab^{odd + even} = ab^{odd},
aoddbodd =abodd+odd=abeven.\begin{array}{r} a^{odd}b^{odd\ } = ab^{odd + odd} = ab^{even}. \end{array}
(1.4.94)

To find all the gen­er­a­tors en­com­pass­ing the sym­met­ric conic group in com­plex space, we remain mind­ful of the de­ter­mi­nant re­sults that occur when the de­fined op­er­a­tion is ap­plied on odd and even per­mu­ta­tions. For ex­am­ple, the op­er­a­tion of mul­ti­pli­ca­tion, with only even de­ter­mi­nant per­mu­ta­tions, will be bound to even de­ter­mi­nants. A way to po­ten­tial­ly de­scribe the min­i­mal el­e­ments of our ma­tri­ces ∈ℂ3\in \mathbb{C}^{3}, is by pro­ject­ing them onto a two-di­men­sion­al com­plex disc. We con­sid­er el­e­ments of the X1X_{1}-type for hy­per­bol­ic forms and spher­i­cal forms, by using the ex­am­ples

X1(Hyperbolic+)=(10000i0−i0),\begin{array}{r} X_{1}\left( Hyperbolic^{+} \right) = \begin{pmatrix} 1 & 0 & 0 \\ 0 & 0 & i \\ 0 & - i & 0 \end{pmatrix}, \end{array}
(1.4.95)
X1(Spherical)=(i0000−1010).\begin{array}{r} X_{1}(Spherical) = \begin{pmatrix} i & 0 & 0 \\ 0 & 0 & - 1 \\ 0 & 1 & 0 \end{pmatrix}. \end{array}
(1.4.96)

We can see the a1,1a_{1,1} en­tries are not only the min­i­mal el­e­ments, but they are also the axes of ro­ta­tion. In the bottom-right 2×22 \times 2 sub­ma­tri­ces are the radial end­points of the min­i­mal el­e­ment mod­u­lus coun­ter­clock­wise (a2,3)\left( a_{2,3} \right), and clock­wise (a3,2)\left( a_{3,2} \right), from the min­i­mal el­e­ment. It should also be noted that the bottom-right sub­ma­trix is the imag­i­nary hy­per­bol­ic analog and the real unit circle analog. Most are fa­mil­iar with the real num­bers rep­re­sent­ing the sub­ma­trix en­tries in the anti-di­ag­o­nal for ℂ→ℝ2\mathbb{C} \rightarrow\mathbb{R}^{2}, but may not be aware that there is a sim­i­lar analog for the split-com­plex num­bers. For these gen­er­a­tors alone, we can raise them to in­te­ger powers, let­ting the min­i­mal el­e­ment cycle through the sub­group el­e­ments. The case for XRe1X_{Re1} is straight­for­ward

{XRe11,XRe12}={(10000i0−i0), (100010001)},\begin{array}{r} \left\{ {X_{Re1}^{1},X}_{Re1}^{2} \right\} = \left\{ \begin{pmatrix} 1 & 0 & 0 \\ 0 & 0 & i \\ 0 & - i & 0 \end{pmatrix},\ \begin{pmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{pmatrix} \right\}, \end{array}
(1.4.97)

for which, we are bound by the pos­i­tive hy­per­bol­ic tan­gent space. For XImag1X_{Imag1}, the min­i­mal el­e­ment cycles the group through all four axes el­e­ments:

{XImag11,XImag12,XImag13,XImag14}={(i0000−1010),   (−1000−1000−1),   (−i000010−10),   (100010001)}.\begin{array}{r} \left\{ X_{Imag1}^{1},X_{Imag1}^{2},X_{Imag1}^{3},X_{Imag1}^{4} \right\} = \left\{ \begin{pmatrix} i & 0 & 0 \\ 0 & 0 & - 1 \\ 0 & 1 & 0 \end{pmatrix},\ \ \ \begin{pmatrix} - 1 & 0 & 0 \\ 0 & - 1 & 0 \\ 0 & 0 & - 1 \end{pmatrix},\ \ \ \begin{pmatrix} - i & 0 & 0 \\ 0 & 0 & 1 \\ 0 & - 1 & 0 \end{pmatrix},\ \ \ \begin{pmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{pmatrix} \right\}. \end{array}
(1.4.98)

These el­e­ments, as two-di­men­sion­al pro­jec­tions, are shown graph­i­cal­ly in Figure 1.4.13, for the iden­ti­ty el­e­ment, the pos­i­tive and neg­a­tive X1X_{1} hy­per­bol­ic tan­gent space, and the tan­gent spaces for the com­plex sphere X1X_{1}-com­po­nent. For all the el­e­ments above, the matrix de­ter­mi­nants are even and bound to the axis num­bers.

Figure
Figure 1.4.13 – Min­i­mal el­e­ments: 1- iden­ti­ty, 2- pos­i­tive hy­per­bol­ic, 3-neg­a­tive hy­per­bol­ic,

4- pos­i­tive spher­i­cal,5- neg­a­tive spher­i­cal.

Turn­ing to the cone number el­e­ments of the X1X_{1}-form, we define the min­i­mal el­e­ment to be

X1(Cone)=((−1)140000i010),\begin{array}{r} X_{1}(Cone) = \begin{pmatrix} ( - 1)^{\frac{1}{4}} & 0 & 0 \\ 0 & 0 & i \\ 0 & 1 & 0 \end{pmatrix}, \end{array}
(1.4.99)

where once again the entry a1,1a_{1,1} rep­re­sents the min­i­mal par­ti­tion el­e­ment and the axis of ro­ta­tion. The min­i­mal par­ti­tion has an odd de­ter­mi­nant, given it is a cone number, and cycles through the entire al­ge­bra set

{X11,X12,X13,X14,X15,X16,X17,X18}={((−1)140000i010),   (i000i000i),   ((−1)340000−10i0),   (−1000−1000−1),(−(−1)140000−i0−10),   (−i000−i000−i),   (−(−1)34000010−i0),   (100010001)}.\begin{array}{r} \left\{ X_{1}^{1},X_{1}^{2},X_{1}^{3},X_{1}^{4},X_{1}^{5},X_{1}^{6},X_{1}^{7},X_{1}^{8} \right\} = \left\{ \begin{array}{r} \begin{pmatrix} ( - 1)^{\frac{1}{4}} & 0 & 0 \\ 0 & 0 & i \\ 0 & 1 & 0 \end{pmatrix},\ \ \ \begin{pmatrix} i & 0 & 0 \\ 0 & i & 0 \\ 0 & 0 & i \end{pmatrix},\ \ \ \begin{pmatrix} ( - 1)^{\frac{3}{4}} & 0 & 0 \\ 0 & 0 & - 1 \\ 0 & i & 0 \end{pmatrix},\ \ \ \begin{pmatrix} - 1 & 0 & 0 \\ 0 & - 1 & 0 \\ 0 & 0 & - 1 \end{pmatrix}, \\ \begin{pmatrix} {- ( - 1)}^{\frac{1}{4}} & 0 & 0 \\ 0 & 0 & - i \\ 0 & - 1 & 0 \end{pmatrix},\ \ \ \begin{pmatrix} - i & 0 & 0 \\ 0 & - i & 0 \\ 0 & 0 & - i \end{pmatrix},\ \ \ \begin{pmatrix} {- ( - 1)}^{\frac{3}{4}} & 0 & 0 \\ 0 & 0 & 1 \\ 0 & - i & 0 \end{pmatrix},\ \ \ \begin{pmatrix} 1 & 0 & 0 \\ 0 & 1 & 0 \\ 0 & 0 & 1 \end{pmatrix} \end{array} \right\}. \end{array}
(1.4.100)
Figure
Figure 1.4.14 – X1X_{1} min­i­mal el­e­ment cone num­bers: (−1)(18) , (−1)(34),( - 1)^{\left( \frac{1}{8} \right)}\ ,\ ( - 1)^{\left( \frac{3}{4} \right)},

−(−1)(14), −(−1)(34){- ( - 1)}^{\left( \frac{1}{4} \right)},\ - ( - 1)^{\left( \frac{3}{4} \right)}, figs. 1,2,3,4, re­spec­tive­ly.

Figure 1.4.14 shows a pro­jec­tive two-di­men­sion­al graph­ic rep­re­sen­ta­tion for the X1X_{1}-type cone num­bers, as they cycle through the quad­rants.

As a final ex­am­ple, we take the min­i­mal el­e­ment (−1)(18)( - 1)^{\left( \frac{1}{8} \right)}, which turns out to be like the (−1)(14)( - 1)^{\left( \frac{1}{4} \right)} ex­am­ple, having a total of 16 el­e­ments in the sub­group, having the (−1)(18)( - 1)^{\left( \frac{1}{8} \right)} min­i­mal el­e­ment matrix rep­re­sen­ta­tion

X1=((−1)180000(−1)14010).\begin{array}{r} X_{1} = \begin{pmatrix} ( - 1)^{\frac{1}{8}} & 0 & 0 \\ 0 & 0 & ( - 1)^{\frac{1}{4}} \\ 0 & 1 & 0 \end{pmatrix}. \end{array}
(1.4.101)

In Figure 1.4.15, shown are four of the el­e­ments on the upper half of the com­plex circle for X1X_{1}, raised to odd powers

{X11,X13,X15,X17}={((−1)180000(−1)14010),((−1)380000i0(−1)140),((−1)580000(−1)340i0),((−1)780000−10(−1)340)}.\begin{array}{r} \left\{ X_{1}^{1},X_{1}^{3},X_{1}^{5},X_{1}^{7} \right\} = \left\{ \begin{pmatrix} ( - 1)^{\frac{1}{8}} & 0 & 0 \\ 0 & 0 & ( - 1)^{\frac{1}{4}} \\ 0 & 1 & 0 \end{pmatrix},\begin{pmatrix} ( - 1)^{\frac{3}{8}} & 0 & 0 \\ 0 & 0 & i \\ 0 & ( - 1)^{\frac{1}{4}} & 0 \end{pmatrix},\begin{pmatrix} ( - 1)^{\frac{5}{8}} & 0 & 0 \\ 0 & 0 & ( - 1)^{\frac{3}{4}} \\ 0 & i & 0 \end{pmatrix},\begin{pmatrix} ( - 1)^{\frac{7}{8}} & 0 & 0 \\ 0 & 0 & - 1 \\ 0 & ( - 1)^{\frac{3}{4}} & 0 \end{pmatrix} \right\}. \end{array}
(1.4.102)
Figure
Figure 1.4.15 – Min­i­mal el­e­ment cones num­bers: (−1)(18) , (−1)(38), (−1)(58), (−1)(78),( - 1)^{\left( \frac{1}{8} \right)}\ ,\ ( - 1)^{\left( \frac{3}{8} \right)},\ ( - 1)^{\left( \frac{5}{8} \right)},\ ( - 1)^{\left( \frac{7}{8} \right)},figs. 1,2,3,4, re­spec­tive­ly.

As men­tioned pre­vi­ous­ly, having a better un­der­stand­ing of the min­i­mal el­e­ments of our group and the con­cept of odd and even de­ter­mi­nants give us better geo­met­ric clar­i­ty con­cern­ing the sym­met­ric conic group. This clar­i­ty is by way of the fact that we will need to start with gen­er­a­tors ∈𝒳,𝒴\in \mathcal{X},\mathcal{Y}, which have odd value de­ter­mi­nants and con­tain the min­i­mal el­e­ment for each.