> < ^ Date: Thu, 07 Jan 1999 12:33:39 +0000 (GMT)
> < ^ From: Alexander Hulpke <hulpke@math.colostate.edu >
^ Subject: Re: a few questions

Dear Gap-Forum,

Ming Chan wrote:

- is there a way to convert from a polynomial to vector? The Polynomial
in Chap. 19 converts vector to poly, but I can't find a command to go
the other way.

In GAP3 (which I assume you use), the command


returns the coefficient list of f. (The shifting is necessary because we
store the coefficient list in a more compact form without leading zeroes.)

(In GAP4 the commands would be:
ShiftedCoefficients(c[1],c[2]); )

- do I refer to an individual element in a vector just the same as I do
in Pascal or C? (eg. vec[0] or vec[1]?)

List access is via the square brackets. However there is no index 0 and
contrary to pascal lists can change their length by adding to them.
The manual chapter on lists explains more details.

- is it possible to do interactive inputs? For example, I want to

In GAP3 this is impossible. (In GAP4 you can acchieve this using streams,
but it is a little bit complicated. You can find example code in the library
file `help.g'.)

- I defined a variable by using:

alpha = Z(256)^1;

which means that alpha is first non-zero Galois field element in
GF(256). From now if I want to a power of alpha I just go alpha^2.
Is it possible to display the name of this variable as "alpha" as well?
Currently the output is displayed as "Z(2^8)^26" or similar, which
reduces readability. I tried using:

alpha.name := "alpha"; 

You cannot change the printing of the built-in finite field elements.

In principle you could acchieve such a result by constructing a field with
256 elements yourself using the command `AlgebraicExtension' (see the manual
for details). Hoever for GAP this field would be different from GF(256) and
it is likely that not all functions will work for these fields. (For example
in GAP3, you cannot multiply matrices over such a field.)

Best regards,

Alexander Hulpke

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