INFINITE PRODUCTS OVER VISIBLE LA’I-I’ICE POINTS
GEOFFREY B. CAMPBELL MathematicsResearch Section
InstituteofAdvanced Studies School of Mathematical Sciences TheAustralianNationalUniversity
GPO Box
4, Canberra, Australia, 2601(Received
August
10, 1992and in revised formSeptember
2,1993)
ABSTRACT.
About fiftynewmultivariatecombinatorial identitiesaregiven,connected withpartition theory,primeproducts,and Dirichlet series. ConnectionstoLatticeSums
inChemistryandPhysicsare alludedtoalso.KEY
WORDS AND
PHRASES:
Combinatorial Identities, Lattice Points in Specified Regions, Riemann’sZeta
Function, Dirichlet Series and otherseriesexpansions.1991 AMS
SUBJECT
CLASSIFICATION CODES:
05A19, llP21, llM06,30B50.1.
INTRODUCTION
Theconceptofvisible-from-the-originlatticepointsin the
X- Y
planewasdescribedinApostol
[2],
where theirdensityin thespacewas calculated. Visiblefromtheorigin latticepoints have thepropertythattheircoordinates are relativelyprime. Recently,ahostofnewidentities werefound,based onsummation orproductstakenonthese points
(see
Campbell
[4],
[5],
[6]).
We presenthere someof the morenotable results fromthesethreepapers,thenextend themtohigherdimensionsgiving general theoremsaccordingly.Firstly,wehave thethree"companion identities,"socalled becauseoftheirinterdependence,and
theirrelation to the visiblefromoriginlattice pointsinthefirstquadrant. Weusetheoperatorsdefined by
where9,isthesetofpositiveintegers less than andrelatively primetok. Thethree"companions" givenin
[4], [5],
and[6]
are(1-y),Hi(1
x:y*)
/(l-Y)
1-)(x,
1)
(1.1)
1-xy
1-1/1
)1/(1
-x)(1-xy),Fl,(1-x
y
=(1-xy
(1.2)
0 x)
(1-y)(1-xy)I-I.(1-xy)’/(1-x
y=(l-y)
t/tt-(1.3)
where
convergence
occursrespectivelyforxy
aridly
[<
1,ix
ariaIxy
I<
1,Ix
andly
l<
1.It
is worthnotingthat theleft side of(1.3)
canbe rewritten)l/b
(l-y) H
(1
x"y
(.,b)-a,b
It
is clear that the identities(1.1),
(1.2)
and(1.3)
belong naturally
togetherwhen we see thatany
one of themimpliesthe othertwo. The reader caneasily verify byiterativemultiplicationon(1.1)
thatxy,
x2y
substitutedfory
leadsto(1.3).
(1.3)
then divided on both sidesby(1.1)
givesnext(1.2).
If y/xis substitutedfory
in(1.2)
weobtain(1.3).
Later
we shall prove generalizations of(1.1)
to(1.3)
both in two dimensions and in higher dimensions. The "companion identity" idea isnot restrictedtojust the aboveformulae.In [6],
for example,the newproductstaken overprimenumbersp
weregivenasfollowsn),I-l(jm
+kn)
#’I-I
I-P4"/"))
,
-p-"
(1.4)
m
+n),IIi(km
+in)
0li(l
_p_+,,
/,,))-u-,-’),
(1.5)
_,)-11-p-)
(1.6)
n
)m
+n),Flijm
+ kn)u’lon
+jn)u
li(I
pvalidwith
p"
,
forrespectivelyRe
m + n andRe
n>l,Re mandRe
m +n >l,Remandren >I.
Theseidentitieswerederivedfrom(I.I)
to(1.3)
bysubstitution of x-p-’,
y
-p-",
andformingtheproduct
overprimesp
oneach side.(1.4)
to(1.6)
ledtoresultsconcerningthemultiplicative
functionco(re,k)-
{-I
1/(l-P2)
with k-lip,-1 a -1
Aswiththeproducts
(1.1)
to(1.3),
weshallgive generalizedversions of(1.4)
to(1.6),
or atleast methods fordoingso.Theunderlyingtheoremsfor theproducts
(1.1)
to(1.3)
wereTHEOREM
1.1. If(a,)
and(b,)
aresequences
of functions chosen so thefollowingseriesconverge,
then1-exp(bkq)
E
Sk,
(1.7)
,.a,
1-exp(b,q/k)
k-1where
Sk
isdefinedbyai, k- 1,
(1.8)
Sk.
jl[.i
,a#,,,
e,,,
exp(bi,hq/k)
k>l(1.9)
and
,
isthesetofsitive
integele than andrelatively primetok.For
aproof
of is seempbell
[4].
(1.1)
derivesom
e
caseofe
theorem wherea,
y*k
-,
b,
klogx
q-.
condly,
a finite vemionofeorem
1.1 was given inmpbell
[5].
EOM
1.2.(a,)
and(b,)
arearbitra
sequences
thorn sothak
mgeer
with choiceof x,thefollowingnctionsareall defined then1-exb)
[--]a,
a + a.,exb.,jx/m)(1.10)
1
exb/k)
where
In
denotestheeatest
integerinn.questionsassociated withthe substitutedfunctionsas n ispermittedtoincrease. Either theorem could be used
(although
Theorem 1.2wasappliedinCampbell
[5])
toobtainnewidentities for Jacobi theta functions. Thediversity of, say(1.10),
is that ityieldsalsoproofs
of classical results such aso_s(n
)(s
+1)-
,
c(n
)k
-l,
Re
s>k,,l
duetoRamanujan,where
os(n
isthe sumofsthpowers
of the divisors of n, andc(n
is themultiplicative functionq(n)-
X
cos Also,in[5],
further results were obtained, such asand,the rather unusualformula for
lq
<1,in which
lyl<l,
exp
4q
2kctsin2kl
1-O,(z,q)=O(z)--
2q’
X
(-1)q’tk
+’)sin(
2k+1)z.
k-o
Evidently thereisscopefor much research on thesetypesof indentities, and whilst Theorems 1.1 and 1.2
may
haveeasilystatedgeneralizationsinhigher dimensions, oreven"companions"in thesense of(1.1),
(1.2),
and(1.3),
in thispaper
weshallspecializealthough
still inhigherdimensions, and obtain numerousnew andsimpleidentities.2.
AN
INFINITE PRODUCT THEOREM IN N-SPACE
In
this section we give ageneraltheorem on multivariate infiniteproductsand a method forobtaining an infinitevarietyof similar theorems. The drawback from thisisthatmostof the other obtainable theoremswillrequireextraefforttoworkout. The ideasregardingcompanion identities as stated in1
mayhelp
us to simply determinewhole classes ofinterdependent formulae in higher dimensional Euclideanspace. We
usethe notation(a,a
,an)
tomean "the greatestcommon divisor ofall ofat,a2
an
together."It
will beimportanttodistinguishbetween this and the orderedn-tuple
givenby thevectornotation(al,
a2,...,an).
In
eithercase we will be concerned with latticepointsintherelevantspace,
henceanyvector orgcdwillbe overintegercoordinates.Theinfiniteproduct
(1.3)
isaparticular case of theTHEOREM
2.1. If 1,2 ,n, then for eachIx,
<1,and bC,
bit
FI
(1 x:’x2...Xn’)
"’
2""
(2.1)
(al,a aa)-afZ
-exp,
lit,.)
provided,-1
DEFINITION
2.2.Any
Euclideanvector(al, a2,...,a)
forwhich(al,a2,...,a)-
wecall avisiblepointvector, abbreviatedvpv.
LEMMA
2.3. Consider aninfiniteregionrayingoutof theorigininanyEuclideanvectorspace.
Thesetofall latticepoint vectorsapart from the originin thatregion isprecisely thesetof positive integer multiples of the visiblepointvectors(vpv’s)
in thatregion.PROOF.
Eachvpvwillhaveintegercoordinateswhosegreatestcommondivisor isunity. Viewed fromtheorigin,all other latticepointsareobscured behindthevpv
endpoints. Ifxis avpv
in theregion then all vectors in thatregionfrom theoriginwith direction ofx preservedareenumerated byasequence
lx,2.x, 3x and thegreatestcommon divisorof thecomponentsof nx isclearlyn. This is because if the scalarn isnon-integeratleastoneof the coordinatesofnx would benon-integer. Therefore,if thevpv’s
in theregionarecountablygivenbyxt,x2,x3 thenall lattice pointvectorsfromtheoriginin theregionarelxt,
2x,
3xlx:, 2x:,,
3x2,..., lx3, 2x,
3x etc.Completionof theproofcomeswithrecognition that thesetof all
vpv’s
inany"rayedfrom the origin" region inanyEuclidean vectorspaceis acountableset. Proofof this last assertionisbyinduction onthedimension, knowingthat the latticepointsare countable in
any
twodimensionalregion.As
we count each latticepointvector in the desiredregionwe decide whetherit isavpv
simply by observingwhether its coordinates arerelativelyprime asawhole. End ofproof.PROOF OF THEOREM
2.1.We
startwith themultiplesumwhich, dueto
Lemma
2.3,alsoequals (lettingb,.
b,)
",.’
....
,.)-1;
+ 2 + 3 + 4 a ab...a,,"
y
’
"
’-1
log(1-
xlx
’ .x’)
(aa,a- .,a,,)- al a2
...an"
if b-1.
Exponentiatingboth sides thenyieldsTheorem 2.1. End ofproof. The caseswithn 2and n 3 are stated easily,in theforms
FI
(1-xy)--’-’-exp
.
?
s+t-l"(2.2)
(a,b
H
(l--xybzC,-"-’b-’c-’---exp{
X’
(a,b,c)-I
i-l?
1--
"
s+t +u -1;
(2.3)
where
Ix
l,
Y
l,
z <1,ands,t,u,arecomplexnumbers.Thecaseof
(2.2)
with s 0 isequivalentto(1.3). In
fact(2.2)
is acompanionto aresultgiveninCampbell
[4],
namely,forpositive integersm,(R)Y’
(ml
iitx’)
(xY)i
g,,,(x)
d--(1
-e:)
-1(2.5)
Iogx
then
(2.4)
holdsforxy
andly
l<
1.Weshallinvestigatesuchcompanionidentities inthenext section.
As
indicatedin 1, such resultscanimplyalarge rangeofnewandcuriousidentities, some ofwhichwerealludedtoinCampbell
[5].
However,
the classical methods ofasymptotics of infiniteproduct generatingfunctions asgiven inAndrews
[1, Chapter 6]
will applytoeachof thenumerousinfiniteproductsstated andimpliedhere. Lemma2.3isalsoapplicabletomanyof thelattice sumsgiveninGlasserandZucker[15]
andtothelattice sumspresentedwithapplicationstomathematicalphysicsas giveninFrankel, Glasser,Hughes
and Ninham
14].
ThelatterpaperappliessimpleMObiusand Mellininversionstolatticesums,obtaining selectedapplicationstoelectrostatics and statisticalmechanics.In
thesequel here,wemay
also drawparallel
conclusionstosomeof the ideas stated in Andrews[1,
Chapter
12]
describingpartitions
intovectors.
In
thepresentpaper
we haveexamplesof"weighted"
vectorpartitions,andquiteadiversity of results.The simplicity ofourproofofTheorem 2.1depended largelyon the factthatourchosen "raying fromorigin" regionwaslhe firsthyperquadrant,that is, theregionhaving allpositiveintegercoordinates inthen-spaceconcerned. This meant wehadnodifficultyinseeingthat themultiplesummation was simply aproductofsummationsof the samekindon the different variables.
For
other choices of"rayed fromorigin" regionsthis isclearlynotsuch astraightforwardmatter.It
is not,however,animpossiblematter.
To
demonstrate this, weapplyLemma
2.3totheregionin3-space
definedby
<X
<Y
<Z,
noting thatitraysoutof theorigininthemannerrequired. The elements of thesetofvectorsfrom the origintothe latticepointsin thisregioncan be easily writtendown,and arecountable, aswewould expect. Thus we have<1,2,3>,
(I,
2,4), (I,
3,4),
<2,
3,4),
<I,
2,5>,
<I,
3,5>,
<I,
4,5>,
<2,
3,5>, <2, 4,5>, <3, 4,5>,
<1,2,
6>, <1,3, 6>, <1,
4,6>,
<1,5, 6>, <2,3, 6>, <2,
4,6>, <2,5, 6>, <3,
4,6>, <3,5, 6>,
<4,5, 6>,
and so on.
A
suitablemappingfrom thesevectorsresultsinthe summation,
x’ybz
c-I(2.6)
O<a<b<c a,b,c
which
formally
reduces toz2/’
xy2(ll-Yt-x
1-x’Y’l
,-1
2+k 1 xy
-"xy
which
converges
for zl,
Y
zl,
[xyz
I<
to(for
non-zerodenominators)
--yz
+.xyz-+
log(1
yz)
+(1 -x)(1
-y)(1 -xy)
(1
-x)(1
-y)
( -x)(
-xy)
log(1
xy
z(1
-y)(1 -xy)
log(1
z).
(2.7)
(2.8)
sum
E
xay
bZcC-1
(a,b,c)-O<a<b
a,b,c
convergent for thesame conditions asthe sum whichled to
(2.7).
ApplicationofLemma 2.3 then transforms(2.8)
into(2.7),
muchin thewayweproved Theorem 2.1. This leadsus toTHEOREM
2.4. Ifx,y,xy
1, and zI,
YZ
[,
[xyz
[<
1,thenFI
(1-x’ybzC)
-/c(1
yz)"
...
(1
xyz)
’’-’’r....
’(1
z)"
"G(x,y,z),
(2.9)
(a,b,c)-O<a<b<c
a,b,c
"
where
yz
G(x,y,z)-exp
-xyzl2"xyz
+-xyz
(1
-x)(1 -y)(1
-xy)Althoughthistheorem looksquite impressive tothe reader newtosuch ideas, itisclearly only comparableto
say,
acorollaryof Theorem2.1whenapparentdepth
anddimensionalityare considered. Theproblemsfaced intryingtomakeTheorem 2.4acorollaryofTheorem 2.1involve: firstly,howto dividethehyperquadrantregionintosubregions,oneofwhich istheregionrelevanttoTheorem2.4; secondly,tothen find theappropriatetransformsothatnotjusttherightregion is covered, but that theindex"-l/c"in theleftsideproductisobtainable.
In many
casesitseems morepracticaltochoose a regionandapplyLemma
2.3,butthere will be situations worthexaminingwhere thehyperspacedivides naturallyintoregions yieldingcompanionidentities.In
ordertoclassifyallsuch identitiesit maybe necessarytousegroup
theoryand isometrics.So
itseemsthat(2.9)
is not inanyobvioussenseacompanion identityfor(2.3),
norforacaseofit. Similarly,this
appears
sofor thefollowing result,obtainedfromsummingonthe latticepointsin theinvertedrightsquare
pyramidIX
andY
]<
Z
in theX
Y Z
space.THEOREM
2.4. Ifx, y,l-x,1-y,areallnon-zero, and eachoflz
l,
xzI,
Iz/x
I,
lY
zl,
Iz/Y
l,
IxY
zI,
Iz/(xY)l,
Ixz/Y
I,
lY
z/x <1,then(1 -z)(1
-xyz)
’
)"’-;)"-"
(1
-xz):(1
yz)
FI
(1
-xybzC)
/(2.10)
(a,b,c
la IbI<cZ,"
a,bz,
Thisresultsuggeststhe existence of ananalogueof Theorem 2.1 where summation is taken over the
vpv’s
and latticepointsin theappropriatelydefinedhyperpyramidin Euclideann-space.
Clearly
thehyperquadrantappears
not toeasilytransform into thehyperpyramid,and viceversa, thus atotally differentsetofcompanionidentitiesareimplied. There are alsoproblemsrelatedtothe consideration of thebranchingeffects of thecomplexrootsinvolved.For
example,inexactlywhichsense do both sidesof(2.10)
satisfythe functionalequationf(x,y,z)
f(1/x,
I/y,I/z)?
3.
NATURAL
CASES
AND
A FURTHER
N-SPACE THEOREM
There are natural andsimplecases ofTheorem 2.1toconsider.
Let
usfirstenlargethetheorem’s positivecoordinatehyperquadranttoincludelatticepointson each axisexceptfor thehighestornth dimension. Thuswecaneasilyobtain thefollowingCOROLLARY
3.1.l/b
I-I
(1
-x"y
(1
y)
-x)(3.1)
(a.t,) a,O,b,l
FI
(l-x’y’z)
/=(l-z)
I/-’)-))H
(I
v"xyza)
TM(I
z)(-’)(-’)(-’)),
{a.b.c.d) a.b c=.O.d,l
H
(I
-vx’y’)
/=(I
))(-’)(-’)()
-)(-’),
( b.c.d.e)= a,b,c.d O,e
eachvalid whenabsolute values of u,
,
x,y,andz are all less than unity. Then-space
veionisthenCOROLRY
3.2. Iffor 1,2n’lx
I<
,h’
.x._z
=(l-z)
-’-’
H
-x x
(a,a..,a)-al.a2. ,an_ I0
al
At
thisim
wecanapplymma
2.3torollary
3.2.In
other words we gel ridofthe criterion onthe left sideproductfrom(3.5)
that(a,a2
a,)
I. We
shallratethe resultofthisas atheoremsincethesubsequentcorollaries willbeof adistinctlydifferent kindfrom our earlier identities.
THEOM
3.3.For
thesame conditions as(3.5)
we haveH
(1-x
x2 ...x.[-zH(1-
(3.6)
a, a._=0 k=
PROOF.
Iftheleftsideof(3.5)
isdefinedbyf(x,x
x
,z)
thenbymma
2.3thistransformsintothe leftsideof
(3.6)
by formingk)l
Applingthe meoperationtotherightsideof
(3.5)
ields
therightsideof(3.6).
End ofproof.
We
canllow ineorem
3.3loobtain someimerestingresulm. Firstly,ifx,
-p
with p denotingthe ithprimewehaveCOROLRY
3.4. IfRe
s>and[z
[<
,,
(1
-xa)
(3.7)
Particularcasesofthisleadtothe Nrther
sin())
v(1
(3.8)
H
(co*))
v*H
(I
z)
4x(3.9)
(sinh(’)
2sinh(’)
co’))
laZ6K)6K
n
(1
+(3.o)
4z
The latter of these results isaffected with the aid of thefollowing product apparently due to
Ramanujan.
If xisanynon-zerocomplex
numberx
sinh(2)-
2sinh()
co)
1+-
4x3
(3.3)
(3.5)
Againemployingthe caseofTheorem 3.3with n and thistimeletting
x,
x’
wecanobtainnew relationsinvolving
p(n),
the number ofunrestricted partitionsof n.It
iswellknown that(see
Andrews
])
?i
Ix
I<
-0 k-I
Likewise, if
po(n
isthenumber ofpartitionsof nintooddpartspo(n)x
17I(1-x2t-)
-l’-go(x),
Ix
l<
1.(3.12)
-0 -1
COROLLARY
3.6.U
lx
andlz
<rl
(1
-xz’)
’)/FI (1
-xX)
x
(3.13)
/,0 k.l
k:,l
1"I
(1
-xz)
’)-
F1(1
-x)
’?
(3.13)
/a0
k,l
Clearly
thereisscopefor further researchintoidentitiessuchasthese, especiallygiven thealready existingwealthofmaterialon partitionidentities.An
alternative versionof(3.13)
for the sameconditions isI’I
(1-xz*)
e)/’l’I
I-I
(1-xa)
’(’/a)/a?(3.15)
l,k,l k,l d]k
Another naturalconcept arising fromthe above workis
p.(j),
the number ofpartitions ofjintopartsat least oneof which isrelatively primetok.In
other words(a,a
a,,k)
1, orequivalentlyana
from and theform taken for such apartitionofjisthenj
-Ala
+A2a
++A.a.,
(for
any m1)
where the
A
are positiveintegerswithoutrestriction. Settingpc.(0):--
1 andemployingour definition, thenallowingn inCorollary
3.2 settingx
-x,theresultfollows thatCOROLLARY
3.7. IfIx
land
Iz
l<
thenforx)as
in(3.11),
),,o,,
n(1
x’z’
--(1-
(3.16)
io
kl
4.
COMPANION IDENTITIES AND VISIBLE POINT VECTOR PARTITIONS
In
the bookon PartitionsbyG.
E.
Andrews 1,Chapter
12]
itisstated that"we
donothave a device likeEuler’s pentagonalnumber theoremfor therapidcalculationofany
multipartitefunctions." The preceding sectionsofthispaper
anditspredecessors[4
to6]
indicatedevelopmentsin this direction, duetotheofteneasy expansionof the functionsconcerned,e.g.
The rightsides of(3.2)
throughto(3.6)
areeasily expanded as
power
series in z. Andrewsmentionshow Carlitz and others[7
to9, and 11,12]
consideredproblemsof restrictedmultipartite partitions.
In
particular, k-partite partitions(nl,
nn,)
(m,i,mi
1-1
subjecttothedecreasingcondition
min(m,,
rnz,...,
rn,)
max(mL
,mz.
,
...,m,.
)
It
isshown in[1]
that ifl-I(n,m)
isthe numberofpartitionsof(n,m)
intosteadilydecreasing partsthenE
H<n,m)x"y"
FI
(1-x"y"-’)-(l-x"-’y")-(l
-xZ"yZ")
-n.m,O n,l
From
this ittbllows easilythat ifI-l<n,m>
isthenumber ofbipartitepartitions of<n,m>
inwhichall parts are of the Ibrms<2a,
2a>or
<a
1, a or<a,
a1>
then forall n and m,l-I<n
,m l-I<n
,m>.
Andrewsstates thatthis resultisofadifferent kindthanthose arisingfrom thesimpleextensionsofpartition
idealsof order considered inhisbook.
In
thelightofourwork inthispaper
itnowbecomes naturaltoconsiderpartitionsinto visiblepoint veclors(vpv’s)
withinrayed-from-origin regionsofvectorspaces.Our
notionof"companion identities," imprecisethoughitbeatthis state,duetoambiguitiesaspresented,willstillbeuseful whenweobtaintheoremsinvolving"the number ofvpv partitions"of various kinds ofvectors.
As
promised in 1,wenowpresentageneralizationof thecompanionidentities(1.1), (1.2),
and(1.3).
CONJECTURE
4.1.Let
sand becomplexandsuch thats+ 1. Thenrespectively
forxy
aridly
I<
1,Ix
and]xy
]<
1,Ix
andly
]<
1,+
(4.2)
(1
-xy)erL(1
-xy)
-
--exp
-,.
(1
-xy),Fl,,(1--x"y)--’b-’(1
--xy
=exp,.,
’’’7
(4.3)
whereit isunderstood that
any
divergent multilogarithmicpowerserieson therightsidescan bereplaced bythe function definedin(2.5).
Partialproof.
(4.3)
isseentobeequivalentto(2.2).
Similarly,(2.4)
isthe case of(4.1)
wherefor positiveintegersm, tn+1.However, (4.1)
claimsconsiderablymorethan(2.4);
namely,thatsand can becomplex
numbers.(4.3)
isobviouslytruefor suchsand t,soitwouldappear
naturalfor(4.1)
tofulfill theseconditions. Since
(4.2)
is asimple quotientof both sides of(4.3)
over(4.1)
it remains onlyfor ustoestablishthat(4.1)
is trueforcomplexsandt.In Campbell
[4]
theproof
of(2.4)depended
onan ruth derivative withrespecttoz logxoff(n,
y
+,,
f(n,x
y’)k
(f(n,
y
f(n,xy
))/(1 -,x
(4.4)
wherentEC
andf(n,y)-
E
y’n-"
with yl<
1. Thisledtok
f(n
+k,xy)g+
(x),
(4.5)
for non-negative integersm andg,(x)
asin(2.5).
Allowingn in thisyields(2.4)
and hence(4.1)
and
(4.2)
for the values tn +Ix. To
fully prove conjecture4.1 wouldrequirecomplex
iteration on thederivativeprocessapplied aboveto(4.4).
End ofpartial proof.It
seems worthnotingat thisstage,having justfailedtoprove conjecture 4.1 completely,that under the conditionsspecifiedthere,Lemma
2.3whenapplied directly gives,H,,(1-x"Y’)-"-’’-’-exp
1-+
"
2,)
++2’+
7
+.-..)4-’,-’
y
y
x yy__
(l-xy)H,(l-x"y
--expxy+and of course,
(4.3).
Thisappearsto addfurther weighttothe likelihoodof conjecture 4.1 beingtrue.It
also shows that the summationsexponentiatedon therightsidesof(4.6)
and(4.7)
are eachvaluable in termsof a finite sum ofmultilogarithms(or
polyiogarithms, see Lewin[16],
and[17])
whenever tn+ fornon-negative integerm, with s + 1. Thiscouldnodoubt bedeveloped
further inalaterpaper.
At
this stage, let usreturn tothe idea ofvectorpartitions.More
specifically,weconsidervpv’s
in the firstquadrantof theX
Y
plane. Basically,thevpv’s
can be divided into threeclasses:a)
those above the lineX
Y,
theuppervpv’s,
b)
those belowand on thelineX
Y,
thelowervpv’s,
c)
thoseof the entirequadrant,that is, allvpv’s.
Weshalltherefore lookat
U(n, m), l.,(n, m), A(n, m);
the number of partitions of(n,m)
intorespectively,upper,
lower,andallvpv’s.
UsingthetechniquesinAndrews],
itisasimplematter toshow that+
U(n,m)x’y"
,FI(I -xy’)
-
(4.8)
+
E
ln,m)x"Y’-(1-xy)-,Fl,(1-x*Yi)
-,
(4.9)
+,,.,.
A<n,m>x"y"
(1
xy)-Fl(1 x’y*)-(1
xy)
-
(4.10)
valid for the samerespectiveconditions onx andy
asimposedon(1.1),
(1.2)
and(1.3).
Each sideof
(4.8)
satisfiesthe functionalequationf(x,y)= f(1/x,xy),
(4.11)
provided
f(1/x,
y
is firsttakenbefore proceedingstof(1/x,xy),
theoperations beingnotcommutative. The coefficients ofy"
in(4.8)
arethepolynomialsm-I
Y.
U(n,m)x
(4.12)
n-I
It
therefore followsnaivelybutsignificantly that,THEOREM
4.2.For
allpositive integers n,m,U(m-
n,m>
U(n,m>.
Thereasoningbehindthistheorem canequallybeappliedtonumerousotherresultsinvolving
vpv
identities.For
example,(4.9)
and(1.2)
bothsatisfythe functionalequation1-x
f(x,
y)
-"x
f(xy,1/y)
(4.13)
where inthiscase
f(x,
1/y)
precedesarrival atf(xy, 1/y). For
thisreason weformalize thefollowingDEFINITION 4.3.
Let
p
bea mapping appliedtoU(n,m), L(n, m), A(n,m),
respectivelytoyieldp<n,
m>,
pt<n,
m>,
p.<n,
m>.
If+
E
<p..,m>x"y"
F(x,y),
(4.14)
+
E
<Pt,
m>xny
=F,.(x,y),
(4.14)
"I-
n,,
(0,,
m)x"y"
F(x,
y)
(4.14)
thenF(x,
y),F(x, y),F(x, y),
arerespectivelycalled"upper vpv",
"lowervpv",
"allvpv"
functions; and likewise(4.14), (4.15),
(4.16),
called"upper vpv",
"lowervpv",
"allvpv"
identities.F(x,xy)
FL(x,
y(4.17)
F^(x,
y,
Fu(x,xy)
(4.18)
F(x,
y)F(x,
yF(x,
y(4.19)
In
otherwords, if givena suitable"upper",
"lower",or"all"vpv identity,we canmanufactureasetof companionidentities.(1.1),
(1.2)
and(1.3)
are essentially anexampleof this. Rather than labor this point, wesimply presentthe"allvpv"
identity resultingfromapplying(4.18)
to(2.4).
THEOREM
4.4. IfIx
andy
[<
1,g(x)
asin(2.5),
andhisany positive integer,theny,
hl(
FI(1-x’y")
a"/"-(1-)exp-g,(x),E
j,
’(1
x’)
+g,(x),
j,.
l_xia,b* d(b)
Thistheorem isanalmostunrecognizable generalizationof
(1.3),
which wouldcoffespondtoe
caseh 0.
It
is distinctfrom the othertypesof "allvpv"
identitiesgivensofar.e
caswithhandh 2are,with
f(n, y)
asin(4.4),
H
(1
-xy)
/exp{xf(E,y)(1
-x)-2
(1
-xy)-
-)(4.21)
(a.b)-a,b
H
(1
-x’y)a%’-exp{-(x
+x:)(1
-x)-3f(3,y)
x(1
-x)-:f(2,y)}
(1
-xy)-t-)
(4.22)
(a.b)-a,b
Yet
another method(and
rhaps the mostobvious)
for manufacturing related"companions"
involvessimplythe
o
equationsFx,y)-F(,y),
andF(x,y)-F(x,).
(4.23)
Whenusingthismethodanadjustmentmaybe madeto
e
firstteofanidentitytotidy ings up. Applying(4.23)
tothe "allvpv"
(2.2)
givesthe"upper"
and"lower" vpvidentities, evenoughey
aretrivially interdependent.cononnv
4.s.u
and are=ompl=xand +,
hit andY
< for(4.Z);
and
l
[<
for(4.25),
then,H,(I-xly’)-’
"-i’exp{(i,)
(i,)
t
(4.24,
(4.)
j’
/j"
is
corolla
hi.lightsthessibilities
forwritingdown differentelatesof companion identities, each tof "companions" having often strikinglydifferentappearance,
evenwheno
distinctcompanionCOROLLARY
4.6.For
respectiveconditionsonxandyasin(1.1),
(1.2),
and(1.3)
wehave(1
+y),l-lj(1
+xy)
/(1
--xY-f-(1-
+Y)]
vt-’)
(1-y)’(l+xy)/
1/(1 2)
(1
+xy
),FI.,(1
+x’y)
l/j..x..y
(1 -xy)
1/(1 2)
(4.26)
(4.27)
_/ l+y
(1 +y)(1
+xy),I-li(1
+x’y’)l/’(1
+xy
--,
(l_y)
Applicationof the same methodto
(2.10)
yields:COROLLARY
4.7.For x, y,
andzas in(2.10),
FI
(1
+x=yz)
/(1
+z)’(1
+xyz)b(1
--X)’(1
--yz)
(.b,)-
(1-z)’(1-xyz)r(1
+xz)(l
+y)
a,b
where a-1,
b-x2y
,
e-x2y(1
+x)(1
+y)-x
2,
d-y2x(1
+x)(1
+y)_yZ,
e-(1 +x)(1
+y)-1,
rxy(l
+x)(
+y)-xy
,
gx:,h-
y
.
It
should be cleartothereader that(4.29)
can,like(2.10),
be derivedom
firstprinciples by taking analtematingsum on thelatticepointsandvpv’s
in therayed-from-origin regionboundedbythe inveed rightsquare
defined inX
Y
Z
space
byXl
andY
I"
Z.
In
mpbell
[4],
similarsuggestionsforobtainingcorollariesweregiven. otherneatcorollary
isobtainedby swappingsand in
(4.25),
thendividingboth sides of this into(4.24),
sothenCOROLRY 4.8.
n
sand arecomplex
with s+ 1,Ix
andly
<1,H{
l_xy
"t-r’
x’y
exp((,
(
(,x’
..k, )).
4.30
e
identitiesof this section show thatmany
of thesimple propertiesof thecompanionidentitiesappear
tobe wohformalizing.For
example,(4.30)
indicatesthat thequotient ofan"upper
v"
with a"lowervpv"
identity
yields(or
isexpected
toyield)
an"allvpv"
identity.
We
continue this sectionby givingasetofcompanionidentities in three dimensionalspace.
In
thisinstance,weconsiderthe firsthyperquadrantof theX
Y
Z
plane includingX
andY
axeswhilst excludingtheZ
axis. fact,if the firsthyperquadrant
istreated as aninfinitely extended cube,then the identities herecoespond
tothe latticepointsin:a)
theextended tetrahedron boundedbyX,Y <Z,
b)
theextendedtetrahedronboundedby
X,Z
Y,
c)
the extended tetrahedronboundedby
Y,Z X,
d)
the entirehyperquadrantwhich isthe unionofa), b),
andc).
TEOM
4.9. ffa andb eachsum overthenon-negativeintegersand c thepositive integers, suchthatfora,b>0,(a,
b,
c)
1 thenH
(1--xaybgC)
-/((1-xz)(1-yz))
1/((1-x)(1-y)),,b,,
(1-z)(1-z)
(4.31)
H
(1
x’yz)
-/((1-z
/(-)t-)(4.32)
....
(1
yz
(4.28)
II
x"
y’z)
-/"z
)-/o
-,,) -,)(4.34)
a,b,c
where the conditions for
convergence
arerespectively,lyzl,
Ixyz
<Il,
lyl,
with variables chosen for non-zero denominator.
PROOF.
In
the usualmannerwe consider thefourlatticesums:a,b b b, a,b,
The last of thesewehave already givenin
(3.2)
asacaseof(2.3)
basically.e
second and ird of theseareeentiallythe me as eachother, by interchange ofxandy.
ey
easilyreducetoe
logarithm of therightsidesof(4.32)
and(4.33)
bye of the summation(I
uand[z
I<
1)
"( z’)
-1 aspan
oftheproce.
e
first lattice sum is((11
-)(1-.)
(4.35)
z
(1-x
*)(1 y)
log
-
(1-x)(1-y)
"(1-x)(1-y)
-z)(1-z)
whichisthelogarithmof therightsideof
(4.31).
Now
eachof the four lattice sums consideredcoespond
tothe aforementioned
"infinitely
extended" tetrahedra which fittogethertomakeupthe firsthyper-quadrant.
such,each tetrahedron is a"rayed
om
origin" region
asains
tomma
2.3.erefore,
applyingmma
2.3toourfourlatticesums, we have forexampleused the first sum that itffansfos into(x"y"’)’/()-
(-1/)og(-x"y"z’),
(a,b,e)-
(a,b,e)-and is establishes
(4.31).
Similarreasoning appliedtoe
otherree
latticesumsgives(4.32 (4.33)
and
(4.34).
Endofproof.
ere
is aninterestingresemblance betweeneorems
4.9and2.4.e
sum(4.35)
showsat
identities like(4.31)
caneasilybegeneralizedto nimensionalspace. Using
sums like(4.35)
e
next few s are,.,.,,
(
z)(
)(
)(
_)
(4.a)
FI
(1-
v"w
’x"y
az
")
-/"a,b,c,d
(a,b,c,d,e)
a,b,c,da0;
(1
vz)(1
wz)(1 -xz)(1
yz)(1
vwxz)
(1
vwyz)
(1
vxyz
(.1.
.-_
wxyz!l
...
"
(1 -z)(1
vwz) (1
vxz) (1
vyz)
(1
wxz) (1
wyz)
(1
x’yz)
(1
vwxyz)
]
(4.37)
where
G (v,
w,x,y)
((1
v) (1
w) (1
x) (1
y))-l"
(4.36)
and(4.37)
needtheabsolute valuesofeach ofz, vz,wz,xz vwz vwxzvwxyz
tobeappropriatelyless thanunity.THEOREM
4.10. IfXo(xt,x2
xn)
andX,(xi,x
xn)
arethesetsofrespectivelyoddandeven number ofproductsof dissimilarxi,...,x,,
then for 1,2 ,nwehave(assuming
X,
actingontheempty
set)
’’
’
.x,’z
)-/"
rI
l-x
x2ex.l-
(4.38)
(at.a
.a,)-ai.a, ,a,,0,a
validfor absolute values of "each elementproductof
Xo
andX,
multipliedbyz"
tobe lessthanunity, and also zl<
1. Alsononeofthex,
areunity.Thistheorem has aninterestingconnection topartition theoryif we permit ntoincreaseindefinitely. After this,letting
x,
x’,
pt(0)
1,p,(0)
0(k
>1)
I,-,’)(,.
2)(,
_,,)..n
-x’z’
-"’’
(
(
-#’(-xzf’’"
,.0.l
(1 -z)(1
=’0(1
-x2z’...
(4.39)
where
pO’)
isthenumber ofpartitionsintopaas
<k,atleast onepa
from1,
Po)
isthenumber ofpaaitions ofjintoan odd number ofdistinctpaas,
p,)
isthe number ofpaitionsofjintoan even number of distinctpas.
However,
Euler’sntagonal
number theorem(see
drews[1,
pp.
10])
statesthatApplyingthistotherightsideof
(4.39)
givesCOROLRY
4.11.fflx
andIz
l<
1,(4.40)
It appears
that the results of this ction arenotthe final word on thetopicofcompanionidentities andvpv
paifions.e
connectionwiththeown
heo
ofpaitions highligMedby
results such as the lattercorollary
also indicatesarichpotentialforNherdevelopment.5.
EULER PRODUCT IDENTITIES AND MULTIPLICATIVE FUNCTIONS
Themethod outlined in
1
forobtaining
(1.4), (1.5),
and(1.6)
is,as surmised fi’omCampbell [6],
capable
ofapplying
toalmost allofthe identities in oursubsequent
sections.Basically
here we revisit[6]
andgivenatural extensions of the results of thatpaper. We
startwiththeDEFINITION
5.1. IfFI[.
jT’
istheprime decompositionofpositive integer kthenfornon-zeroml, m2,
(5.2)
In [6]
the functionfrom(5.1)
was showntonaturallyoccur in the Dirichlet seriesresulting from(1.4),
(1.5),
and(1.6).
For
example,(1.6)
isequivalenttothestatementFI
(j’m+kn)
-la’.
h(k)Oal(m,k)
Rern
and Ren>l.(5.4)
o$, k
In
thisX(k)=
I-I;.
t(-1)"
isLiouville’s arithmetic function(for
an account of this function see Chart-drasekharan10]).
Given the results of ourpresentpaper,wecanderiveDirichletseriesgeneratingfunctions for the multiplicativefunctions ofDefinition5.1. Firstly applyingtheproduct operator
H
toeachsideof theidentities inCorollaries3.1 and3.2,wehave, letting each variable,sayx bereplaced by
p-*
beforeemployingtheproduct operator,THEOREM
5.2. IfRe
tn andRe
n > thenandgenerally
H
(arni
+bn)-/b=
Y.
k)tot(mt,
k)
O,b,,1 k-I k
(a,b)-El
(amt
+bin+cn)
-t/*,
X(k)(mt’m2"k)
a,b.0;c k"
(a,b,c)-I-[
(am
+bin +cm+dn)
-I/ak(k)J3(tnl’m2"m3’k)
a,b,e.0;d
(a,b,c,d)
(5.5)
(5.6)
(5.7)
H
(arn
+brn:,
+cn)
-/rI(1
-p-)/((-’"’)(-’-’))
a,b O,c p
(a,b,)
From
here wesimplyexpandtherightsideof(5.9)
intotheappropriateDirichlet seriesleadingto(5.6).
Thismethod can bejustaswellappliedtothe other identities in
Corollary
5.2. End ofproof.
Identities suchas(5.9)
can be written down immediatelyfrommany
of the identities already presented here;forexample(4.36)
implies(5.9)
onboth sidesgives
H
H(1
-pa,b,0; p
(a,b,)-which isequivalentto
II(1-p-*)
El
(alm
+a:zm
+...+ahm+an)
-/,
X(’k)ch(m’m2’""m"k).
(5.8)
a O’,a k
(at,a.2.,
I-I
(a.b.c,d)-a,b,cl O,d
(ami
+ bm.,+ cm +dn)-t/a.
I-I(
(I -p-)(l
-p-"
+"
+))(I
p-"’
+"/"))
’
(1
p-0,,, +"))
(1
p-"
+"))
(1
(1
p4,,,/,,,,/,,))
(I
-p’+"’
*"
/"’/"))
(5.10)
valid for real parts ofthe following: n,mt+n,m2+n,m3+n,
m
+ m2 +n,m
+m3 +n, m2+ m3 + n, mt+m2 +m +n, allgreaterthanunity. Alsoml,m2,m3,n are*0.In [6],
summationssuch as(5.5)
weregivensomeinterpretation, showingthat our functioncot(re,k)
occursnaturallyineach ofthecompanionidentities
(1.4),
(1.5), (1.6). In
ordertoproperly
find inter-pretationsof the"primeproducts" presented
itisnecessarytouse theTHEOREM
5.3. IfRe(ira
+kn)
> forpositive integerk thenO’m
+kn)a/
=,.
f,(r)
r,,,+,
(5.11)
thenwith
r)
the Liouville function,(-1/kl=
r)
(-’/kl
(5.12)
.,(r)
1.1I1(-1
)’
a,
,.
a,
’
where
{I
p istheprime decompositionofpositive integerr.For
aproof
of this see[6],
however theproof
iselementaryand based on nothing more than thebinomialtheorem and theEulerproductformof the Riemannzetafunction. Theorem5.3holdsan
important keytointerpretingmanyof the identities of our present work.
It
isclear from(5.12)
that,,(r)
isreally onlyafunction oftypef(r),
andsoforinstancethe function under theproduct operationonleft sideof
(5.10)
is(ami
+bm2
+cm
+dn)-t/a
]’(r)
(5.13)
am
+bm + cm + dnIn
applyingthemethods of[6]
tothehigherdimensional caseswestraightaway
runintoformal difficultiesunless we chooseappropriateidentitiestoexamine.It
seems that the identitiesofCorollaries 3.1 and3.2 againarise, further supportingour assertion in{}3
thatthey representa classof"naturalcases"
ofTheorem2.1. Although thejof,,(r)
in(5.12)
isseento besuperfluousweshall finditusefultokeepas a means ofidentifyingthat this function arisesfor the(jm +
kn)
function.We
willdistinguish thenbetween functionsgenerated by(l"m
+kn)
and(j2m
+kn).
Indeed,for thehigherdimensional cases we will introducefurther parameterstoany
.,(r),
makingitsay
f,,,:,i,(r),
when arising for(am
+bm2
+ cm3 +jm+kn)/.
Thisallowsustoidentifythesource of the Dirichletgenerated coef-ficientsshouldtheyhave same values as other coefficient functions in theproducts.At
thispointwegiveourtheorem,whichessentially equatesDirichlet coefficientsof
(5.8).
We
firstwill needtogivea definition.DEFINITION
5.4.Consider the latticepointarrivedatfrom theoriginbythevector(ai,
a2,...,a).
t(N (N
o
(m
t,m
m,N
I-I
f,,l.,
(N<a’
a2’ah))N<al’
a2ah)-"l’l
h-l"-l)(5.14)
a,, .a_ 0(a,%,
,a)-with the summatio over all solutionsof
al,, ,ah_ 0
ah
where allbut afinit,umberof the
N<a,
aa
areunityandonlythenon-unityfactors are considered for(5.14) (
istheMobiusfunction).
PROOF.
isssentially parallelstheproof
of thanalogousrsultiven
in[6].
W
startom
the finiteproducton the
int8r
seuenc
(i),
1, j h,)/’
This iseasily
proved
byinduction on s. All paaial productsontherightsideof(5.14)
areofthis kindsincethelattice
ints
inthehyperquadrantconcernedarecountable(recall
ourproofofmma
2.3in2).
Ifk isany positive integerthe coefficientofk"
in(5.16)
isdeteinedom
those tesr[
"
whichare factors of k-.
otherwords,the Dirichletgenerated
coefficientof k"
inwherethe summation is over each solution ofk
H.
r,
’.In (5.16)
wemay
choose the asequence
toconform withthe latticeints
in theproduct
operators of(5.14)
and(5.15),
owingtothecountabilityof the latticepointsinthis"rayed
om
origin" region.Hence
the product operatorof(5.1
transforms into that of(5.14)
and(5.15),
andwecanallow stoincrease indefinitely.
e
Mobius Nnction onthe leftsideof(5.14)
isdue toour consideringe
reciprocal identityof(5.8)
inordertobetterapply(5.11)
totheanalysis. is ise
formalproo e
stipulationin the theorem that"allbut a finitenumber of theN(a,a,...,a
areunity"
simplymeans that,whilstanyteundertheproduct
operatormay
benon-unity,be it the millionthteore
firstteinthepaaialproduct,eachproductunder the summation in
(5.14)
is considered finite. Of coume theleft side of(5.14)comes
om
thereciprocal identityproduced
om
(5.8)
ingMobius inveion. Endofproof.
It
is important to undetand thateorem
5.5 is essentially a multidimensional factorization theorem where each visible latticeint
intheregionisallowed anarbitrarysitive
integervalue raisedtoa cemin
power,
and allssible
productsof such numbe areconsidered,g
ineorem
5.5werake theexample
whereN
is aprime,thecomplexityreducestoasimpleresult.(5.14)
isbasicallya mul-tidimensional Dirichlet summationrepresentationofthe arithmetic Nnction on its left side.e
case whereh 2ofeorem
5.5wasgivenaspaa
ofatheorem in[6].
6.
CONCLUDING
REMARKS
thatafullclassificationofthe identities hereinwouldamount toaclassification ofsymmetricrotations inarbitrarydimensionallattices;notasimplematter. Nevertheless,thevpvideaexemplifiedin
Lemma
2.3 isapplicabletoany rayed-from-origin Euclidean region. Wehaveshown that classesofinterde-pendent vpvidentities existprobablyinanydimension,andthereappearstobeavarietyof methods for obtainingthese.
A
consistent theoretical approachtoclassification of "companion identities" would seemdesirableatthisstage,giventhatwehavenowopenedthedoortoasensible multivariateworld.In
thispaperwehave refrainedfromentering deeplyintoparticular logarithmicderivatives of the products. Alsowehavenotfully exploredtheinterestingconvergence boundary
casesofmanyresults. Wehavenotyetfollowedup higherdimensionalanaloguesin the moregeneralsenseofTheorems 1.1 and1.2, whichleadus tonumerous results onRamanujan typearithmetic functions on the onehand, and Jacobithetafunctionresults on theother.Future
work onvpv identitiesmayinvolvelatticesumsofchemistryaspresentedinGlasserand Zucker[15],
applicationstothetheoryofpartitions,orsome of thevpvworkmayfindapplicationinadditive numbertheory. Thislatter seems a naturalapplication since additive functions are invariant
undersomeofthetransformsin thispaper. Assuch,vpvmethodsmaybe linked tosomeof theproblems given in Elliott 13,pp.330-341
].
ACKNOWLEDGEMENT.
Theauthor is indebtedto: ProfessorR.J.Baxter,
who kindly arrangedVisitor
Status
and accessatAustralian NationalUniversity;ProfessorG. E.
Andrews,whosethoughtful and positiveresponsehas beenacatalyst;Dr.
Peter Forrester
whowasalwaysin therightmathematical place,besidesbeingasourceof encouragement.REFERENCES
ANDREWS, G. E.
(1976).
TheTheoryof Partitions Vol.2, Encyclopediaof Mathematics anditsApplications, Addison-Wesley.
[2]
APOSTOL, T. M.
(1976).
IntroductiontoAnalyticNumberTheory,
Springer-Verlag,New
York.[3]
BERNDT.
B. C.
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