## 90 Reputation

9 years, 123 days

## How to transform a permutation into numb...

Maple 15

Dear all,

I hope everyone helps me about the problem of converting a permutation into numbers and vice versa on maple

Let Sn denote the set of all permutations of the set {0, 1, ..., n − 1}

Lehmer code is a bijective function l : Sn ->{0, 1, 2, ..., n! − 1}.

Define function l(S)=Sum(ci x (n − 1 − i)! ) where S in Sn and ci is the number of elements of the set { j > i | sj < si }

Inverse Lehmer code is a bijective function l−1 : {0, 1, 2, ..., n! − 1} -> Sn

For example: n=4 -->{0, 1, 2, 3}, for S = (0, 2, 1, 3) , so c0 = 0, c1 = 1 ( j=2 > i=1 and sj = 1 < si = 2), c2 = 0, c3 = 0 -->

I(S) = 0 x (3-0)! + 1 x (3 - 1)! + 0 x (3-2)! + 0 x (3 - 3)! = 2! = 2. So I((0, 2, 1, 3)) =2  and I-1(2) = (0, 2, 1, 3).

How to calculate I and I-1 on maple? Please help me! Thanks alot.

## How to compute an extension of finite fi...

Hi EveryOne!

In the answer of the question "How to find roót of polynomial in finite field and extension finite field ", @Carl Love helped me to find roots of polynimial in finite field and extension finite field (At URL http://www.mapleprimes.com/view.aspx?sf=215097_Answer/Primfield.mw OR http://www.mapleprimes.com/view.aspx?sf=215285_Answer/Matrix_powers_finite_field.mw)

However, with matrix M: =< x^4+x^3+x^6+x^7+x, 1+x^2+x^4+x^5+x^6, 1+x+x^2+x^3, x^7+x^6+x^5+x^4;

x^7+x^5+x^4+x^3, x^6+x^4+x^2+1, x^4+x^3+x^6+x^7+x^2+x+1, 1+x^2+x^3+x^4+x^5;

x^7+x^5+x^2, x^7+x^5+x^3+x^2+1, x^2+x+x^6, x^2+x^3+x^5;
x^4+x^3+x^6+1, 1+x^2+x^3+x^4, x^6+x^5+x^4+x^3, x^7+x^3 >;

and GF(2^8)/f(x)=x^8 + x^7 +x^6 + x +1 (i.e ext1:= Z^8+Z^7+Z^6+Z+1), then program Primfield.mw don't run!

## How to convert to matrix over finite fie...

Maple

Hi all

I need to convert int matrix into matrix over finite field.

E.g: Convert inform integer number

A := <140, 155, 162, 64;

218, 12, 245, 50;

36, 251, 34, 253;

171, 251, 184, 37>;

into B = <x^7+x^3+x^2,x^7+x^4+x^3+x+1,x^7+x^5+x, x^6;

x^7+x^6+x^4+x^3+x, x^3+x^2, x^7+x^6+x^5+x^4+x^2+1, x^5+x^4+x;

x^5+x^2, x^7+x^6+x^5+x^4+x^3+x+1, x^5+x, x^7+x^6+x^5+x^4+x^3+x^2+1;

x^7+x^5+x^3+x+1, x^7+x^6+x^5+x^4+x^3+x+1, x^7+x^5+x^4+x^3, x^5+x^2+1>;

(Matrix B over finite field GF(2^8)/f(x) =x^8 + x^6 +x^5 +x^3 +1)

Thanks alot.

## Three questions on matrices...

Maple

Hi EveryOne!

Let matrix M over GF(2n)/f(x). How to compute:

1. Rank of M.

2. Sum of the elements and Square of this Sum in any row of M (i.e: Sum=mi0 + mi1 + ... + min, and Sum2 ).

3. New matrix M, where in row i  mi0 = mi0/Sum2, mi1 = mi1/Sum2, ..., min = min/Sum2.

## How to compute direct exponentiation of ...

Maple

Hi EveryOne!

In the the answer of the question "How to find k^th root of the given matrix over finite field (at URL: http://www.mapleprimes.com/questions/203997-How-To-Find-Kth-Root-Of-The-Given-Matrix#comment215683). Carl Love helped to find k^th root of the given matrix M over GF(2m)/f(x).

Now, I need to compute direct exponentiation of the given matrix M in finite field. (If M = [mi,j], we say Direct Exponent (element-wise exponent matrix), Mdk of M is a matrix whose each element is the result of exponentiation of corresponding elements of M. If k=2, then we say Md2 is a direct square matrix of M )