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--All rights reserved.
--
--Redistribution and use in source and binary forms, with or without
--modification, are permitted provided that the following conditions are
--met:
--
-- - Redistributions of source code must retain the above copyright
-- notice, this list of conditions and the following disclaimer.
--
-- - Redistributions in binary form must reproduce the above copyright
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-- the documentation and/or other materials provided with the
-- distribution.
--
-- - Neither the name of The Numerical ALgorithms Group Ltd. nor the
-- names of its contributors may be used to endorse or promote products
-- derived from this software without specific prior written permission.
--
--THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS
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--EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO,
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)abbrev category LALG LeftAlgebra
++ Author: Larry A. Lambe
++ Date : 03/01/89; revised 03/17/89; revised 12/02/90.
++ Description: The category of all left algebras over an arbitrary
++ ring.
LeftAlgebra(R:Ring): Category == Join(Ring, LeftModule R) with
--operations
coerce: R -> %
++ coerce(r) returns r * 1 where 1 is the identity of the
++ left algebra.
add
coerce(x:R):% == x * 1$%
)abbrev domain EAB ExtAlgBasis
--% ExtAlgBasis
++ Author: Larry Lambe
++ Date created: 03/14/89
++ Description:
++ A domain used in the construction of the exterior algebra on a set
++ X over a ring R. This domain represents the set of all ordered
++ subsets of the set X, assumed to be in correspondance with
++ {1,2,3, ...}. The ordered subsets are themselves ordered
++ lexicographically and are in bijective correspondance with an ordered
++ basis of the exterior algebra. In this domain we are dealing strictly
++ with the exponents of basis elements which can only be 0 or 1.
-- Thus we really have L({0,1}).
++
++ The multiplicative identity element of the exterior algebra corresponds
++ to the empty subset of X. A coerce from List Integer to an
++ ordered basis element is provided to allow the convenient input of
++ expressions. Another exported function forgets the ordered structure
++ and simply returns the list corresponding to an ordered subset.
ExtAlgBasis(): Export == Implement where
I ==> Integer
L ==> List
NNI ==> NonNegativeInteger
Export == OrderedSet with
coerce : L I -> %
++ coerce(l) converts a list of 0's and 1's into a basis
++ element, where 1 (respectively 0) designates that the
++ variable of the corresponding index of l is (respectively, is not)
++ present.
++ Error: if an element of l is not 0 or 1.
degree : % -> NNI
++ degree(x) gives the numbers of 1's in x, i.e., the number
++ of non-zero exponents in the basis element that x represents.
exponents : % -> L I
++ exponents(x) converts a domain element into a list of zeros
++ and ones corresponding to the exponents in the basis element
++ that x represents.
-- subscripts : % -> L I
-- subscripts(x) looks at the exponents in x and converts
-- them to the proper subscripts
Nul : NNI -> %
++ Nul() gives the basis element 1 for the algebra generated
++ by n generators.
Implement == add
Rep := L I
x = y == x =$Rep y
x < y ==
null x => not null y
null y => false
first x = first y => rest x < rest y
first x > first y
coerce(li:(L I)) ==
for x in li repeat
if not one? x and not zero? x then
error "coerce: values can only be 0 and 1"
li
degree x == (_+/x)::NNI
exponents x == copy(x @ Rep)
-- subscripts x ==
-- cntr:I := 1
-- result: L I := []
-- for j in x repeat
-- if j = 1 then result := cons(cntr,result)
-- cntr:=cntr+1
-- reverse! result
Nul n == [0 for i in 1..n]
coerce(x: %) == coerce(x @ Rep)$(L I)
)abbrev domain ANTISYM AntiSymm
++ Author: Larry A. Lambe
++ Date : 01/26/91.
++ Revised : 30 Nov 94
++
++ based on AntiSymmetric '89
++
++ Needs: ExtAlgBasis, FreeModule(Ring,OrderedSet), LALG, LALG-
++
++ Description: The domain of antisymmetric polynomials.
AntiSymm(R:Ring, lVar:List Symbol): Export == Implement where
LALG ==> LeftAlgebra
FMR ==> FM(R,EAB)
FM ==> FreeModule
I ==> Integer
L ==> List
EAB ==> ExtAlgBasis -- these are exponents of basis elements in order
NNI ==> NonNegativeInteger
O ==> OutputForm
base ==> k
coef ==> c
Term ==> Record(k:EAB,c:R)
Export == Join(LALG(R), RetractableTo(R)) with
leadingCoefficient : % -> R
++ leadingCoefficient(p) returns the leading
++ coefficient of antisymmetric polynomial p.
-- leadingSupport : % -> EAB
leadingBasisTerm : % -> %
++ leadingBasisTerm(p) returns the leading
++ basis term of antisymmetric polynomial p.
reductum : % -> %
++ reductum(p), where p is an antisymmetric polynomial,
++ returns p minus the leading
++ term of p if p has at least two terms, and 0 otherwise.
coefficient : (%,%) -> R
++ coefficient(p,u) returns the coefficient of
++ the term in p containing the basis term u if such
++ a term exists, and 0 otherwise.
++ Error: if the second argument u is not a basis element.
generator : NNI -> %
++ generator(n) returns the nth multiplicative generator,
++ a basis term.
exp : L I -> %
++ exp([i1,...in]) returns \spad{u_1\^{i_1} ... u_n\^{i_n}}
homogeneous? : % -> Boolean
++ homogeneous?(p) tests if all of the terms of
++ p have the same degree.
retractable? : % -> Boolean
++ retractable?(p) tests if p is a 0-form,
++ i.e., if degree(p) = 0.
degree : % -> NNI
++ degree(p) returns the homogeneous degree of p.
map : (R -> R, %) -> %
++ map(f,p) changes each coefficient of p by the
++ application of f.
-- 1 corresponds to the empty monomial Nul = [0,...,0]
-- from EAB. In terms of the exterior algebra on X,
-- it corresponds to the identity element which lives
-- in homogeneous degree 0.
Implement == FMR add
Rep := L Term
x,y : EAB
a,b : %
r : R
m : I
dim := #lVar
1 == [[ Nul(dim)$EAB, 1$R ]]
coefficient(a,u) ==
not null u.rest => error "2nd argument must be a basis element"
x := u.first.base
for t in a repeat
if t.base = x then return t.coef
if t.base < x then return 0
0
retractable?(a) ==
null a or (a.first.k = Nul(dim))
retractIfCan(a):Union(R,"failed") ==
null a => 0$R
a.first.k = Nul(dim) => leadingCoefficient a
"failed"
retract(a):R ==
null a => 0$R
leadingCoefficient a
homogeneous? a ==
null a => true
siz := +/exponents(a.first.base)
for ta in reductum a repeat
+/exponents(ta.base) ~= siz => return false
true
degree a ==
null a => 0$NNI
homogeneous? a => (+/exponents(a.first.base)) :: NNI
error "not a homogeneous element"
zo : (I,I) -> L I
zo(p,q) ==
p = 0 => [1,q]
q = 0 => [1,1]
[0,0]
getsgn : (EAB,EAB) -> I
getsgn(x,y) ==
sgn:I := 0
xx:L I := exponents x
yy:L I := exponents y
for i in 1 .. (dim-1) repeat
xx := rest xx
sgn := sgn + (+/xx)*yy.i
sgn rem 2 = 0 => 1
-1
Nalpha: (EAB,EAB) -> L I
Nalpha(x,y) ==
i:I := 1
dum2:L I := [0 for i in 1..dim]
for j in 1..dim repeat
dum:=zo((exponents x).j,(exponents y).j)
(i:= i*dum.1) = 0 => leave
dum2.j := dum.2
i = 0 => cons(i, dum2)
cons(getsgn(x,y), dum2)
a * b ==
null a => 0
null b => 0
((null a.rest) and (a.first.k = Nul(dim))) => a.first.c * b
((null b.rest) and (b.first.k = Nul(dim))) => b.first.c * a
z:% := 0
for tb in b repeat
for ta in a repeat
stuff:=Nalpha(ta.base,tb.base)
r:=first(stuff)*ta.coef*tb.coef
if r ~= 0 then z := z + [[rest(stuff)::EAB, r]]
z
coerce(r):% ==
r = 0 => 0
[ [Nul(dim), r] ]
coerce(m):% ==
m = 0 => 0
[ [Nul(dim), m::R] ]
characteristic == characteristic$R
generator(j) ==
-- j < 1 or j > dim => error "your subscript is out of range"
-- error will be generated by dum.j if out of range
dum:L I := [0 for i in 1..dim]
dum.j:=1
[[dum::EAB, 1::R]]
exp(li:(L I)) == [[li::EAB, 1]]
leadingBasisTerm a ==
[[a.first.k, 1]]
displayList:EAB -> O
displayList(x):O ==
le: L I := exponents(x)$EAB
reduce(_*,[(lVar.i)::O for i in 1..dim | one?(le.i)])$L(O)
makeTerm:(R,EAB) -> O
makeTerm(r,x) ==
-- we know that r ~= 0
x = Nul(dim)$EAB => r::O
one? r => displayList(x)
-- r = 0 => 0$I::O
-- x = Nul(dim)$EAB => r::O
r::O * displayList(x)
coerce(a):O ==
zero? a => 0$I::O
null rest(a @ Rep) =>
t := first(a @ Rep)
makeTerm(t.coef,t.base)
reduce(_+,[makeTerm(t.coef,t.base) for t in (a @ Rep)])$L(O)
)abbrev domain DERHAM DeRhamComplex
++ Author: Larry A. Lambe
++ Date : 01/26/91.
++ Revised : 12/01/91.
++
++ based on code from '89 (AntiSymmetric)
++
++ Needs: LeftAlgebra, ExtAlgBasis, FreeMod(Ring,OrderedSet)
++
++ Description: The deRham complex of Euclidean space, that is, the
++ class of differential forms of arbitary degree over a coefficient ring.
++ See Flanders, Harley, Differential Forms, With Applications to the Physical
++ Sciences, New York, Academic Press, 1963.
DeRhamComplex(CoefRing,listIndVar:List Symbol): Export == Implement where
CoefRing : Join(Ring, OrderedSet)
ASY ==> AntiSymm(R,listIndVar)
DIFRING ==> DifferentialRing
LALG ==> LeftAlgebra
FMR ==> FreeMod(R,EAB)
I ==> Integer
L ==> List
EAB ==> ExtAlgBasis -- these are exponents of basis elements in order
NNI ==> NonNegativeInteger
O ==> OutputForm
R ==> Expression(CoefRing)
Export == Join(LALG(R), RetractableTo(R)) with
leadingCoefficient : % -> R
++ leadingCoefficient(df) returns the leading
++ coefficient of differential form df.
leadingBasisTerm : % -> %
++ leadingBasisTerm(df) returns the leading
++ basis term of differential form df.
reductum : % -> %
++ reductum(df), where df is a differential form,
++ returns df minus the leading
++ term of df if df has two or more terms, and
++ 0 otherwise.
coefficient : (%,%) -> R
++ coefficient(df,u), where df is a differential form,
++ returns the coefficient of df containing the basis term u
++ if such a term exists, and 0 otherwise.
generator : NNI -> %
++ generator(n) returns the nth basis term for a differential form.
homogeneous? : % -> Boolean
++ homogeneous?(df) tests if all of the terms of
++ differential form df have the same degree.
retractable? : % -> Boolean
++ retractable?(df) tests if differential form df is a 0-form,
++ i.e., if degree(df) = 0.
degree : % -> I
++ degree(df) returns the homogeneous degree of differential form df.
map : (R -> R, %) -> %
++ map(f,df) replaces each coefficient x of differential
++ form df by \spad{f(x)}.
totalDifferential : R -> %
++ totalDifferential(x) returns the total differential
++ (gradient) form for element x.
exteriorDifferential : % -> %
++ exteriorDifferential(df) returns the exterior
++ derivative (gradient, curl, divergence, ...) of
++ the differential form df.
Implement == ASY add
Rep := ASY
dim := #listIndVar
totalDifferential(f) ==
divs:=[differentiate(f,listIndVar.i)*generator(i)$ASY for i in 1..dim]
reduce("+",divs)
termDiff : (R, %) -> %
termDiff(r,e) ==
totalDifferential(r) * e
exteriorDifferential(x) ==
x = 0 => 0
termDiff(leadingCoefficient(x)$Rep,leadingBasisTerm x) + exteriorDifferential(reductum x)
lv := [concat("d",string(liv))$String::Symbol for liv in listIndVar]
displayList:EAB -> O
displayList(x):O ==
le: L I := exponents(x)$EAB
reduce(_*,[(lv.i)::O for i in 1..dim | one?(le.i)])$L(O)
makeTerm:(R,EAB) -> O
makeTerm(r,x) ==
-- we know that r ~= 0
x = Nul(dim)$EAB => r::O
one? r => displayList(x)
r::O * displayList(x)
terms : % -> List Record(k: EAB, c: R)
terms(a) ==
-- it is the case that there are at least two terms in a
a pretend List Record(k: EAB, c: R)
coerce(a):O ==
a = 0$Rep => 0$I::O
ta := terms a
-- reductum(a) = 0$Rep => makeTerm(leadingCoefficient a, a.first.k)
null ta.rest => makeTerm(ta.first.c, ta.first.k)
reduce(_+,[makeTerm(t.c,t.k) for t in ta])$L(O)
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