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|
BindGlobal( "CollectPolycyclicGap", function( pcp, ev, w )
local ngens, pow, exp, com, wst, west, sst, est, bottom,
stp, g, word, exponent, i, h, m, u, j, cnj,
icnj, hh;
if Length( w ) = 0 then return true; fi;
ngens := pcp![PC_NUMBER_OF_GENERATORS];
pow := pcp![ PC_POWERS ];
exp := pcp![ PC_EXPONENTS ];
com := pcp![ PC_COMMUTE ];
wst := [ ];
west := [ ];
sst := [ ];
est := [ ];
bottom := 0;
stp := bottom + 1;
wst[stp] := w;
west[stp] := 1;
sst[stp] := 1;
est[stp] := w[ 2 ];
# collect
while stp > bottom do
if est[stp] = 0 then
# initialise est
sst[stp] := sst[stp] + 1;
if sst[stp] > Length(wst[stp])/2 then
west[stp] := west[stp] - 1;
if west[stp] <= 0 then
## clear stacks before going down
wst[ stp ] := 0;
west[ stp ] := 0;
sst[ stp ] := 0;
est[ stp ] := 0;
stp := stp - 1;
else
sst[stp] := 1;
est[stp] := wst[stp][2];
fi;
else
est[stp] := wst[stp][ 2*sst[stp] ];
fi;
else
# get next generator
g := wst[stp][ 2*sst[stp]-1 ];
if stp > 1 and sst[stp] = 1 and g = com[g] then
## collect word ^ exponent in one go
word := wst[stp];
exponent := west[stp];
## Add the word into ev
for i in [1,3..Length(word)-1] do
h := word[ i ];
ev[h] := ev[h] + word[ i+1 ] * exponent;
od;
## Now reduce.
for h in [word[1]..ngens] do
if IsBound( exp[h] ) and ev[h] >= exp[h] then
m := QuoInt( ev[h], exp[h] );
ev[h] := ev[h] mod exp[h];
if IsBound( pow[h] ) then
u := pow[h];
for j in [1,3..Length(u)-1] do
ev[ u[j] ] := ev[ u[j] ] + u[j+1] * m;
od;
fi;
fi;
od;
west[ stp ] := 0;
est[ stp ] := 0;
sst[ stp ] := Length( word );
elif g = com[g] then
# move generator directly to its correct position
ev[g] := ev[g] + est[stp];
est[stp] := 0;
else
if est[stp] > 0 then
est[stp] := est[stp] - 1;
ev[g] := ev[g] + 1;
cnj := pcp![ PC_CONJUGATES ];
icnj := pcp![ PC_INVERSECONJUGATES ];
else
est[stp] := est[stp] + 1;
ev[g] := ev[g] - 1;
cnj := pcp![ PC_CONJUGATESINVERSE ];
icnj := pcp![ PC_INVERSECONJUGATESINVERSE ];
fi;
h := com[g];
# Find first position where we need to collect
while h > g do
if ev[h] <> 0 then
if ev[h] > 0 then
if IsBound( cnj[h][g] ) then break; fi;
else
if IsBound( icnj[h][g] ) then break; fi;
fi;
fi;
h := h-1;
od;
# Put that part on the stack, if necessary
if h > g or
( IsBound(exp[g])
and (ev[g] < 0 or ev[g] >= exp[g])
and IsBound(pow[g]) ) then
for hh in [com[g],com[g]-1..h+1] do
if ev[hh] <> 0 then
stp := stp+1;
if ev[hh] > 0 then
wst[stp] := pcp![ PC_GENERATORS ][hh];
west[stp] := ev[hh];
else
wst[stp] := pcp![ PC_INVERSES ][hh];
west[stp] := -ev[hh];
fi;
sst[stp] := 1;
est[stp] := wst[stp][ 2 ];
ev[hh] := 0;
fi;
od;
fi;
# move generator across the exponent vector
while h > g do
if ev[h] <> 0 then
stp := stp+1;
if ev[h] > 0 then
if IsBound( cnj[h][g] ) then
wst[stp] := cnj[h][g];
west[stp] := ev[h];
else
wst[stp] := pcp![ PC_GENERATORS ][h];
west[stp] := ev[h];
fi;
else
if IsBound( icnj[h][g] ) then
wst[stp] := icnj[h][g];
west[stp] := -ev[h];
else
wst[stp] := pcp![ PC_INVERSES ][h];
west[stp] := -ev[h];
fi;
fi;
sst[stp] := 1;
est[stp] := wst[stp][ 2 ];
ev[h] := 0;
fi;
h := h-1;
od;
fi;
# reduce exponent if necessary
if IsBound( exp[g] ) and ev[g] >= exp[g] then
ev[g] := ev[g] - exp[g];
if IsBound( pow[g] ) then
stp := stp+1;
wst[stp] := pow[g];
west[stp] := 1;
sst[stp] := 1;
est[stp] := wst[stp][ 2 ];
fi;
fi;
fi;
od;
return true;
end );
BindGlobal( "PrintCollectionStack", function( stp, wst, west, sst, est )
while stp > 0 do
Print( wst[stp], "^", west[stp],
" at ", sst[stp], " with exponent ", est[stp], "\n" );
stp := stp - 1;
od;
end );
#############################################################################
##
#M CollectWordOrFail . . . . . . . . . . . . . . . . . . . . . . . . . . . .
##
InstallMethod( CollectWordOrFail,
"FromTheLeftCollector (outdated)",
[ IsFromTheLeftCollectorRep,
IsList, IsList ],
function( pcp, ev, w )
Error( "Collector is out of date" );
end );
InstallMethod( CollectWordOrFail,
"FromTheLeftCollector",
[ IsFromTheLeftCollectorRep and IsUpToDatePolycyclicCollector,
IsList, IsList ],
function( pcp, a, b )
if USE_LIBRARY_COLLECTOR then
return CollectPolycyclicGap( pcp, a, b );
else
# CollectPolycyclic is implemented by the GAP C kernel, in file src/objcftl.c
CollectPolycyclic( pcp, a, b );
return true;
fi;
end );
InstallMethod( CollectWordOrFail,
"FromTheLeftCollector",
[ IsFromTheLeftCollectorRep and IsUpToDatePolycyclicCollector and
UseLibraryCollector,
IsList, IsList ],
CollectPolycyclicGap );
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