module compact; % Header module for compact code.
% Author: Anthony C. Hearn.
% Copyright (c) 1989 The RAND Corporation. All Rights Reserved.
create!-package('(compact mv mvmatch reddom compactf comfac),
'(contrib compact));
endmodule;
module mv; % Operations on multivariate forms.
% Author: Anthony C. Hearn.
% Copyright (c) 1989 The RAND Corporation. All Rights Reserved.
symbolic smacro procedure mv!-!.!+(u,v); u . v;
symbolic smacro procedure mv!-!.!*(u,v); u . v;
symbolic smacro procedure mv!-lc u; cdar u;
symbolic smacro procedure mv!-lpow u; caar u;
symbolic smacro procedure mv!-lt u; car u;
symbolic smacro procedure mv!-red u; cdr u;
symbolic smacro procedure mv!-term!-coeff u; cdr u;
symbolic smacro procedure mv!-term!-pow u; car u;
symbolic smacro procedure mv!-tpow u; car u;
symbolic smacro procedure mv!-tc u; cdr u;
symbolic procedure mv!-!+(u,v);
if null u then v
else if null v then u
else if mv!-lpow u= mv!-lpow v
then (lambda x;
if x=0 then mv!-!+(mv!-red u,mv!-red v)
else mv!-!.!+(mv!-!.!*(mv!-lpow u,x),
mv!-!+(mv!-red u,mv!-red v)))
(mv!-lc u + mv!-lc v)
else if mv!-pow!-!>(mv!-lpow u,mv!-lpow v)
then mv!-!.!+(mv!-lt u,mv!-!+(mv!-red u,v))
else mv!-!.!+(mv!-lt v,mv!-!+(u,mv!-red v));
symbolic smacro procedure domain!-!*(u,v); u*v;
symbolic smacro procedure domain!-!/(u,v); u/v;
symbolic procedure mv!-term!-!*(u,v);
% U is a (non-zero) term and v a multivariate form. Result is
% product of u and v.
if null v then nil
else mv!-!.!+(mv!-!.!*(mv!-pow!-!+(mv!-tpow u,mv!-lpow v),
domain!-!*(mv!-tc u,mv!-lc v)),
mv!-term!-!*(u,mv!-red v));
symbolic procedure mv!-term!-!/(u,v);
% Returns the result of the (exact) division of u by term v.
if null u then nil
else mv!-!.!+(mv!-!.!*(mv!-pow!-!-(mv!-lpow u,mv!-tpow v),
domain!-!/(mv!-lc u,mv!-tc v)),
mv!-term!-!/(mv!-red u,v));
symbolic procedure mv!-domainlist u;
if null u then nil
else mv!-lc u . mv!-domainlist mv!-red u;
symbolic procedure mv!-pow!-mv!-!+(u,v);
if null v then nil
else mv!-!.!+(mv!-pow!-mv!-term!-!+(u,mv!-lt v),
mv!-pow!-mv!-!+(u,mv!-red v));
symbolic procedure mv!-pow!-mv!-term!-!+(u,v);
mv!-!.!*(mv!-pow!-!+(u,mv!-term!-pow v), mv!-term!-coeff v);
symbolic procedure mv!-pow!-!+(u,v);
if null u then nil
else (car u+car v) . mv!-pow!-!+(cdr u,cdr v);
symbolic procedure mv!-pow!-!-(u,v);
if null u then nil
else (car u-car v) . mv!-pow!-!-(cdr u,cdr v);
symbolic procedure mv!-pow!-!*(u,v);
if null v then nil
else (u*car v) . mv!-pow!-!*(u,cdr v);
symbolic procedure mv!-pow!-minusp u;
if null u then nil
else car u<0 or mv!-pow!-minusp cdr u;
symbolic procedure mv!-pow!-!>(u,v);
if null u then nil
else if car u=car v then mv!-pow!-!>(cdr u,cdr v)
else car u>car v;
symbolic procedure mv!-reduced!-coeffs u;
% reduce coefficients of u to lowest terms.
begin scalar x,y;
x := mv!-lc u;
y := mv!-red u;
while y and x neq 1 do <<x := gcdn(x,mv!-lc y); y := mv!-red y>>;
return if x=1 then u else mv!-!/(u,x)
end;
symbolic procedure mv!-!/(u,v);
if null u then nil
else mv!-!.!+(mv!-!.!*(mv!-lpow u,mv!-lc u/v),mv!-!/(mv!-red u,v));
% Functions that convert between standard forms and multivariate forms.
symbolic procedure sf2mv(u,varlist);
% Converts the standard form u to a multivariate form wrt varlist.
sf2mv1(u,nil,varlist);
symbolic procedure sf2mv1(u,powers,varlist);
if null u then nil
else if domainp u
then list(append(powers,nzeros length varlist) . u)
else if mvar u = car varlist % This should be eq, but seems to
% need equal.
then append(sf2mv1(lc u,append(powers,list ldeg u),cdr varlist),
sf2mv1(red u,powers,varlist))
else sf2mv1(u,append(powers,list 0),cdr varlist);
symbolic procedure nzeros n; if n=0 then nil else 0 . nzeros(n-1);
symbolic procedure mv2sf(u,varlist);
% converts the multivariate form u to a standard form wrt varlist.
% This version uses addf to fold terms - there is probably a more
% direct method.
if null u then nil
else addf(mv2sf1(mv!-lpow u,cdar u,varlist),mv2sf(cdr u,varlist));
symbolic procedure mv2sf1(powers,cf,varlist);
if null powers then cf
else if car powers=0 then mv2sf1(cdr powers,cf,cdr varlist)
else !*t2f((car varlist .** car powers)
.* mv2sf1(cdr powers,cf,cdr varlist));
endmodule;
module mvmatch; % Side relation matching against expressions.
% Author: Anthony C. Hearn.
% Copyright (c) 1991 The RAND Corporation. All Rights Reserved.
symbolic procedure mv!-compact(u,v,w);
% Compares a multivariate form u with a multivariate form template v
% and reduces u appropriately.
% Previously, the content was removed from u. However, this does
% not work well if the same content is in v.
begin scalar x,y; % z;
if null u then return mv!-reverse w;
% if null w then <<z := mv!-content u; u := mv!-term!-!/(u,z)>>
% else z := nzeros length mv!-lpow u . 1;
% check first terms.
if (x := mv!-pow!-chk(u,v))
and (y := mv!-compact2(u,mv!-pow!-mv!-!+(x,v)))
% then return mv!-term!-!*(z,mv!-compact(y,v,w))
then return mv!-compact(y,v,w)
% check second terms.
else if (x := mv!-pow!-chk(u,mv!-red v))
and not mv!-pow!-assoc(y := mv!-pow!-!+(x,mv!-lpow v),w)
and (y := mv!-compact2(mv!-!.!+(mv!-!.!*(y,0),u),
mv!-pow!-mv!-!+(x,v)))
% then return mv!-term!-!*(z,mv!-compact(y,v,w))
% else return mv!-term!-!*(z,mv!-compact(mv!-red u,v,mv!-lt u . w))
then return mv!-compact(y,v,w)
else return mv!-compact(mv!-red u,v,mv!-lt u . w)
end;
symbolic procedure mv!-pow!-assoc(u,v); assoc(u,v);
symbolic procedure mv!-reverse u; reversip u;
symbolic procedure mv!-pow!-chk(u,v);
% (u := mv!-pow!-!-(caar u,caar v)) and not mv!-pow!-minusp u and u;
if v and (u := mv!-pow!-!-(caar u,caar v)) and not mv!-pow!-minusp u
then u
else nil;
symbolic procedure mv!-compact2(u,v);
% U and v are multivariate forms whose first powlists are equal.
% Value is a suitable multiplier of v which when subtracted from u
% results in a more compact expression.
begin scalar x,y,z;
x := equiv!-coeffs(u,v);
z := mv!-domainlist v;
y := reduce(x,z);
return if y=x then nil
else mv!-!+(mv!-coeff!-replace(v,mv!-domainlist!-!-(y,x)),u)
end;
symbolic procedure mv!-coeff!-replace(u,v);
% Replaces coefficients of multivariate form u by those in domain
% list v.
if null u then nil
else if car v=0 then mv!-coeff!-replace(mv!-red u,cdr v)
else mv!-!.!+(mv!-!.!*(mv!-lpow u,car v),
mv!-coeff!-replace(mv!-red u,cdr v));
symbolic procedure equiv!-coeffs(u,v);
if null u then nzeros length v
else if null v then nil
else if mv!-lpow u = mv!-lpow v
then cdar u . equiv!-coeffs(cdr u,cdr v)
else if mv!-pow!-!>(mv!-lpow u,mv!-lpow v)
then equiv!-coeffs(cdr u,v)
else 0 . equiv!-coeffs(u,cdr v);
endmodule;
module reddom; % Reduction of domain elements.
% Author: Anthony C. Hearn.
% Copyright (c) 1989 The RAND Corporation. All Rights Reserved.
fluid '(mv!-vars!*);
global '(!*xxx !*yyy);
switch xxx,yyy;
!*xxx := !*yyy := t;
% Operations on domain elements.
symbolic smacro procedure domain!-!+(u,v); u+v;
symbolic smacro procedure domain!-!-(u,v); u-v;
symbolic smacro procedure domain!-!*(u,v); u*v;
symbolic smacro procedure domain!-divide(u,v); divide(u,v);
% Operations on domain element lists.
symbolic procedure mv!-domainlist!-!+(u,v);
if null u then nil
else domain!-!+(car u,car v) . mv!-domainlist!-!+(cdr u,cdr v);
symbolic procedure mv!-domainlist!-!-(u,v);
if null u then nil
else domain!-!-(car u,car v) . mv!-domainlist!-!-(cdr u,cdr v);
symbolic procedure mv!-domainlist!-!*(u,v);
if null v then nil
else domain!-!*(u,car v) . mv!-domainlist!-!*(u,cdr v);
% Procedures for actually reducing domain elements.
symbolic procedure reduce(u,v);
% Reduce domain element list u with respect to an equal length domain
% element list v. We assume that v has been reduced to lowest terms.
begin scalar weightlist,x;
% Look for equal ratios of elements.
x := u;
if !*yyy then
x := reduce!-ratios(x,v);
% Define weighting list.
weightlist := set!-weights v;
% Choose column elimination with lowest weight.
if !*xxx then
x := reduce!-columns(x,v,weightlist);
% Look for a reduction in weight of the expression.
if !*xxx then
x := reduce!-weights(x,v,weightlist);
return x
end;
symbolic procedure set!-weights v;
% Define weights to be associated with the reduction test.
% The current definition is pretty naive.
begin integer n;
% return reversip for each j in v collect (n := n+1)
return reversip (0 . for each j in cdr v collect 1)
end;
symbolic procedure reduce!-ratios(u,v);
begin scalar x;
if null(x := red!-ratios1(u,v)) then return u;
x := mv!-domainlist!-!-(mv!-domainlist!-!*(car x,u),
mv!-domainlist!-!*(cdr x,v));
return if zeros u >= zeros x then u
else reduce!-ratios(x,v)
end;
symbolic procedure zeros u;
if null u then 0
else if car u = 0 then 1+zeros cdr u
else zeros cdr u;
symbolic procedure red!-ratios1(u,v);
u and (red!-ratios2(cdr u,cdr v,car u,car v)
or red!-ratios1(cdr u,cdr v));
symbolic procedure red!-ratios2(u,v,u1,v1);
begin integer n;
return if null u then nil
else if (n := u1*car v) = v1*car u and n neq 0
then red!-lowest!-terms(v1,u1)
else red!-ratios2(cdr u,cdr v,u1,v1)
end;
symbolic procedure red!-lowest!-terms(u,v);
begin scalar x;
if u<0 then <<u := -u; v := -v>>;
x := gcdn(u,v);
% We must have x = u otherwise the reduction has the
% wrong factor.
if x neq u then errach list("red-lowest-terms",u,v);
return 1 . (v/x)
end;
symbolic procedure reduce!-columns(u,v,weightlist);
begin scalar w,x,y,z,z1;
x := u;
y := v;
w := (u . red!-weight(u,weightlist));
a: if null x then return car w
else if car x=0 or car y=0 then nil
else if cdr(z := domain!-divide(car x,car y))=0
then <<z := mv!-domainlist!-!-(u,mv!-domainlist!-!*(car z,v));
z1 := red!-weight(z,weightlist);
if red!-weight!-less!-p(z1,cdr w)
and not more!-apartp(z . z1,w)
then w := (z . z1)>>;
x := cdr x;
y := cdr y;
go to a
end;
symbolic procedure more!-apartp(u,v);
cadr u=2 and cadr u=cadr v and cadar u=0 and cadar v neq 0;
symbolic procedure reduce!-weights(u,v,weightlist);
begin scalar success,x,y,z;
x := red!-weight(u,weightlist);
a: y := mv!-domainlist!-!+(u,v);
z := red!-weight(y,weightlist);
if red!-weight!-less!-p(z,x)
then <<success := t; u := y; x := z; go to a>>;
if success then return u;
b: y := mv!-domainlist!-!-(u,v);
z := red!-weight(y,weightlist);
if red!-weight!-less!-p(z,x) then <<u := y; x := z; go to b>>;
return u
end;
symbolic procedure red!-weight(u,weightlist);
nonzero!-length u . red!-weight1(u,weightlist);
symbolic procedure red!-weight1(u,weightlist);
if null u then 0
else abs car u*car weightlist
+ red!-weight1(cdr u,cdr weightlist);
symbolic procedure nonzero!-length u;
if null u then 0
else if car u=0 then nonzero!-length cdr u
else add1 nonzero!-length cdr u;
symbolic procedure red!-weight!-less!-p(u,v);
if car u=car v then cdr u<cdr v else car u<car v;
endmodule;
module compactf; % Algorithms for compacting algebraic expressions.
% Author: Anthony C. Hearn.
% Copyright (c) 1991 The RAND Corporation. All Rights Reserved.
fluid '(mv!-vars!*);
global '(!*trcompact);
switch trcompact;
% Interface to REDUCE simplifier.
put('compact,'simpfn,'simpcompact);
symbolic procedure simpcompact u;
begin scalar bool;
if null u or null cdr u
then rerror(compact,1,
list("Wrong number of arguments to compact"));
if null !*exp then <<rmsubs(); bool := !*exp := t>>;
u := errorset!*(list('simpcompact1,mkquote u),nil);
if bool then !*exp := nil;
if errorp u then rerror(compact,2,"Compact error");
return car u
end;
symbolic procedure simpcompact1 u;
begin scalar v,x;
v := simp!* car u;
u := cadr u;
if idp u
then if eqcar(x := get(u,'avalue),'list)
then u := cadr x
else typerr(u,"list")
else if getrtype u eq 'list then u := cdr u
else typerr(u,"list");
u := for each j in u collect if not eqcar(j,'equal) then j
else !*eqn2a j;
for each j in u do v := compactsq(v,simp!* j);
return v
end;
% True beginning of compacting routines.
symbolic procedure compactsq(u,v);
% U is a standard quotient, v a standard quotient for equation v=0.
% Result is a standard quotient for u reduced wrt v=0.
begin
if denr v neq 1
then msgpri("Relation denominator",prepf denr v,"discarded",
nil,nil);
v := numr v;
return multsq(compactf(numr u,v) ./ 1,
1 ./ compactf(denr u,v))
end;
symbolic procedure compactf(u,v);
% U is a standard form, v a standard form for an equation v=0.
% Result is a standard form for u reduced wrt v=0.
begin scalar x; integer n;
if !*trcompact
then <<prin2t "*** Arguments on entering compactf:";
mathprint mk!*sq !*f2q u;
mathprint mk!*sq !*f2q v>>;
while x neq u do <<x := u; u := compactf1(u,v); n := n+1>>;
if !*trcompact and n>2
then <<prin2 " *** Compactf looped ";prin2 n; prin2t " times">>;
return u
end;
symbolic procedure compactf1(u,v);
begin scalar x,y,z;
x := kernels u;
y := kernels v;
z := intersection(x,y); % find common vars.
if null z then return u;
% Unfortunately, it's too expensive in space to generate all perms.
% as in this example:
% l:={-c31*c21+c32*c22+c33*c23+c34*c24=t1};
% x:= -c31*c21+c32*c22+c33*c23+c34*c24;
% compact(x,l); % out of heap space
% for each j in permutations z do u := compactf11(u,v,x,y,j);
return compactf11(u,v,x,y,z)
% return u
end;
symbolic procedure compactf11(u,v,x,y,z);
begin scalar w;
if domainp u then return u;
y := append(z,setdiff(y,z)); % vars in eqn.
x := append(setdiff(x,z),y); % all vars.
x := setkorder x;
u := reorder u; % reorder expressions.
v := reorder v;
z := comfac!-to!-poly comfac u;
u := quotf(u,z);
u := remchkf(u,v,y);
w := compactf2(u,mv!-reduced!-coeffs sf2mv(v,y),y);
if termsf w < termsf u then u := w;
% Should we also reduce z at this point?
u := multf(z,u);
% It is possible that if z is not a kernel product, that including
% z in the reduction can lead to a more compact form, but we
% exclude that case for the time being.
setkorder x;
u := reorder u;
if !*trcompact
then <<prin2t "*** Value on leaving compactf11:";
mathprint mk!*sq !*f2q u>>;
return u
end;
symbolic procedure remchkf(u,v,vars);
% This procedure returns u after checking if a smaller remainder
% results after division by v. It is potentially inefficient, since
% we check all the way down the list, term by term. However, the
% process terminates when we no longer have any relevant kernels.
(if domainp x or null intersection(kernels u,vars) then x
else lt x .+ remchkf(red x,v,vars))
where x=remchkf1(u,v);
symbolic procedure remchkf1(u,v);
begin integer n;
n := termsf u;
v := xremf(u,v,n);
if null v or termsf(v := car v)>=n then return u
else if !*trcompact then prin2t "*** Remainder smaller";
return v
end;
symbolic procedure xremf(u,v,m);
% Returns the quotient and remainder of U divided by V, or NIL if
% the number of terms in the remainder exceeds M.
% The goal is to keep terms u+terms z<=m.
% There is some slop in the count, so one must check sizes on
% leaving.
begin integer m1,m2,n; scalar x,y,z;
if domainp v then return list cdr qremd(u,v);
m2 := termsf u;
a: if m<= 0 then return nil
else if domainp u then return list addf(z,u)
else if mvar u eq mvar v
then if (n := ldeg u-ldeg v)<0 then return list addf(z,u)
else <<x := qremf(lc u,lc v);
y := multpf(lpow u,cdr x);
m := m+m1;
z := addf(z,y);
m1 := termsf z;
m := m-m1+m2;
u := if null car x then red u
else addf(addf(u,multf(if n=0 then v
else multpf(mvar u .** n,v),
negf car x)), negf y);
m2 := termsf u;
m := m-m2;
go to a>>
else if not ordop(mvar u,mvar v) then return list addf(z,u);
m := m+m1;
x := xremf(lc u,v,m);
if null x then return nil;
z := addf(z,multpf(lpow u,car x));
m1 := termsf z;
m := m-m1;
u := red u;
go to a
end;
symbolic procedure compactf2(u,v,vars);
% U is standard form for expression, v for equation. W is ordered
% list of variables in v. Result is a compacted form for u.
if domainp u then u
else if mvar u memq vars then compactf3(u,v,vars)
else lpow u .* compactf2(lc u,v,vars) .+ compactf2(red u,v,vars);
symbolic procedure compactf3(u,v,vars);
begin scalar mv!-vars!*;
mv!-vars!* := vars;
return mv2sf(mv!-compact(sf2mv(u,vars),v,nil),vars)
end;
endmodule;
module comfac; % Multivariate common factor/content routines.
% Author: Anthony C. Hearn.
% Copyright (c) 1989 The RAND Corporation. All Rights Reserved.
symbolic smacro procedure domain!-gcd(u,v); gcdn(u,v);
symbolic smacro procedure domain!-onep u; onep u;
symbolic procedure mv!-pow!-zerop u;
null u or zerop car u and mv!-pow!-zerop cdr u;
symbolic procedure mv!-pow!-gcd(u,v);
if null u then nil
else min(car u,car v) . mv!-pow!-gcd(cdr u,cdr v);
symbolic procedure mv!-content u;
% Finds the term that is the content of u.
if null u then nil
else begin scalar x,y;
x := mv!-lc u;
y := mv!-lpow u;
a: u := mv!-red u;
if null u or domain!-onep x and mv!-pow!-zerop y
then return mv!-!.!*(y,x);
x := domain!-gcd(x,mv!-lc u);
y := mv!-pow!-gcd(y,mv!-lpow u);
go to a
end;
endmodule;
end;