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module groebopt;
 
%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%%
%   optimization of the sequence of variables
%
 
% Optimization of variable sequence; 
% the theoretical background can be found
% in  Boege/Gebauer/Kredel , J.Symb.Comp(1986)I,83-98
% Techniques modfied to the following algorithm
%
% x > y if
%  x appears in a higher power than y
%       or
%  the highest powers are equal, but x appears more often with 
% that power.
%
% An explicit dependency DEPENDS X,Y will supersede the optimality.
 
fluid '(vdpvars!*     % list of intersting variables (and korder)
        intvdpvars!*
        !*trgroeb     % control of print messages
       );
 
symbolic procedure vdpvordopt (w,vars);
  % w : list of polynomials (standard forms)
  % vars: list of variables
  % returns (w . vars), both reorderdered
  begin; scalar c;
        vars := sort(vars,'ordop);
        c := for each x in vars collect x . 0 . 0;
        for each poly in w do vdpvordopt1 (poly,vars,c);
        c := sort(c,function vdpvordopt2);
        intvdpvars!* := for each v in c collect car v;
	vars := vdpvordopt31 intvdpvars!*;
        if !*trgroeb then
        <<prin2 "optimized sequence of kernels: "; prin2t vars>>;
        return (for each poly in w collect reorder poly) . vars;
  end;
 
symbolic procedure vdpvordopt1 (p,vl,c);
   if null p then 0
      else
   if domainp p or null vl then 1
      else
   if mvar p neq car vl then vdpvordopt1(p,cdr vl,c)
      else
   begin scalar var,pow,slot; integer n;
      n := vdpvordopt1 (lc p,cdr vl,c);
      var := mvar p;
      pow := ldeg p;
      slot := assoc(var,c);
      if pow #> cadr slot then
          <<rplaca(cdr slot,pow); rplacd(cdr slot,n)>>
        else
          rplacd(cdr slot,n #+ cddr slot);
      return n #+ vdpvordopt1 (red p,vl,c);
   end;
 
symbolic procedure vdpvordopt2(sl1,sl2);
  % compare two slots from the power table
    <<sl1 := cdr sl1;
      sl2 := cdr sl2;
      car sl1 #< car sl2 or car sl1 = car sl2 and cdr sl1 #< cdr sl2
    >>;
 
symbolic procedure vdpvordopt31 u;
   % u : list of variables
   % returns u reordered to respect dependency ordering
   begin scalar v,y;
   if null u then return nil;
   v := foreach x in u join
      	<< y := assoc(x,depl!*);
 	   if null y or null xnp(cdr y,u) then {x} >>;
   return nconc(vdpvordopt31 setdiff(u,v),v);
   end;

% symbolic procedure vdpvordopt3(x,y);
%   % two level compare: 1. dependency, 2. optimal order.
%      depends(x,y) or member(y,member(x,intvdpvars!*));

endmodule;
 
end;