File r37/packages/poly/reord.red artifact 76b967149e part of check-in f2fda60abd

module reord; % Functions for reordering standard forms.

% Author: Anthony C. Hearn.

% Copyright (c) 1990 The RAND Corporation.  All rights reserved.

fluid '(alglist!* kord!* ncmp!*);

alglist!* := nil . nil;         % This is first module that uses this.

symbolic procedure reordsq u;
   % Reorders a standard quotient so that current kernel order is used.
   reorder numr u ./ reorder denr u;

symbolic procedure reorder u;
   % Reorders a standard form so that current kernel order is used.
   % Note: this version does not reorder any sfs used as kernels.
   if domainp u then u
    else raddf(rmultpf(lpow u,reorder lc u),reorder red u);

symbolic procedure raddf(u,v);
   % Adds reordered forms U and V.
   if null u then v
    else if null v then u
    else if domainp u then addd(u,v)
    else if domainp v then addd(v,u)
    else if peq(lpow u,lpow v)
     then (lpow u .* raddf(lc u,lc v)) .+ raddf(red u,red v)
    else if ordpp(lpow u,lpow v) then lt u . raddf(red u,v)
    else lt v . raddf(u,red v);

symbolic procedure rmultpf(u,v);
  % Multiplies power U by reordered form V.
   if null v then nil
    else if domainp v or reordop(car u,mvar v) then !*t2f(u .* v)
    else (lpow v .* rmultpf(u,lc v)) .+ rmultpf(u,red v);

symbolic procedure reordop(u,v);
   if ncmp!* and noncomp u and noncomp v then t else ordop(u,v);

symbolic procedure kernel!-list u;
  % Converts u to a list of kernels, expanding lists in u.
  for each x in u join
   <<x:=reval x; 
     if eqcar(x,'list) then kernel!-list cdr x else {!*a2k x}>>;

symbolic procedure korder u;
   <<kord!* := if u = '(nil) then nil else kernel!-list u;
     rmsubs()>>;

rlistat '(korder);

symbolic procedure setkorder u;
   begin scalar v;
      v := kord!*;
      if u=v then return v;
      kord!* := u;
      alglist!* := nil . nil;        % Since kernel order has changed.
      return v
   end;

symbolic procedure updkorder u;
   % U is a kernel.  Value is previous kernel order.
   % This function is used when it is necessary to give one kernel
   % highest precedence (e.g., when extracting coefficients), but not
   % change the order of the other kernels.
   begin scalar v,w;
      v := kord!*;
      w := u . delete(u,v);
      if v=w then return v;
      kord!* := w;
      alglist!* := nil . nil;        % Since kernel order has changed.
      return v
   end;

endmodule;

end;