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Dear Forum,

last week, Anatolii Rukolaine wrote

I tested two years ago the program to compute character table

described in the GAP-manual section Dixon-Schneider "An Example of Advanced

Calculations" and I had some problems for some finite groups, for example, for

G:=MathieuGroup(22) of Order 443520 and for G:=PrimitiveGroup(8,4) of Order 336

(=PGL(2,7)).After comments

"...#Finally we calculate the characters induced from all cyclic subgroups

# and obtain the missing irreducibles by applying the LLL-algorithm to them."and after GAP-commands:

ic:= InducedCyclic( c, "all" );;

ro:= ReducedOrdinary( c, c.irreducibles, ic );;and before GAP-command:

l:= LLL( c, ro.remainders );;I received the message:

Error, List Element: <list>[1] must have a value at

B := [ scpr( L, b[1], b[1] ) ] ... in

LLLReducedBasis( arg[1], arg[2], y ) called from

LLL( c, ro.remainders ) called from

main loop

brk>

Thanks for reporting this deficiency of the command `LLL'.

In GAP 4, this function will accept also an empty list

as second argument.

Concerning the remarks about the manual section about

``An Example of Advanced Dixon Schneider Calculations'',

it is not the aim of this section to present a recipe

that is useful for arbitrary finite groups.

Just the contrary, the calculations shown there assume

interactive use of GAP, since the user has to decide

what functions might return something that is useful

in the context of Dixon Schneider calculations.

Perhaps this aspect should be emphasized in the manual

for the next version of GAP.

By the way, the reported problems to compute the

character tables of M22 and PGL(2,7) refer only to

the try to calculate the tables of these groups

exactly along the lines of the example in the manual.

Computing these tables with the default strategy

used by `CharTable' requires only a few seconds

on a (semi-)modern PC.

Kind regards,

Thomas

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