2018-12-15 13:46:52 -0600 received badge ● Nice Question (source) 2018-12-15 12:16:38 -0600 commented answer How to express unknown coefficients in GF(2^8)? thank you so much! this is exactly what I need 2018-12-15 12:16:12 -0600 received badge ● Supporter (source) 2018-12-15 12:16:10 -0600 received badge ● Scholar (source) 2018-12-15 11:05:29 -0600 received badge ● Editor (source) 2018-12-15 10:32:46 -0600 asked a question How to express unknown coefficients in GF(2^8)? I want to make computations in GF(2^8) using the Rijndael modulus X^8+X^4+X^3+X+1 and with unknown elements of GF(2^8). For example, I need a polynomial x which is defined as x = x_7 * X^7 + x_6 * X^6 + x_5 * X^7 + ... + x_0 x.coefficients() should return [x_0, x_1, x_2, x_3, x_4, ...] If I for example add x to y, I would expect that the result would be a term like (x_7+y_7) * X^7 + (x_6+y_6)*X^6 + ... I tried the following: sage: pgen = polygen(Integers(2)) sage: modulus = pgen()**8 + pgen()**4 + pgen()**3 + pgen() + 1 sage: F = FiniteField(2**8, 'X', modulus = modulus) sage: X = F.gen() X sage: x_coeffs = list(var('x_%d' % i) for i in range(8)) sage: y_coeffs = list(var('y_%d' % i) for i in range(8)) sage: uF = PolynomialRing(F, 16, x_coeffs + y_coeffs); uF Multivariate Polynomial Ring in x_0, x_1, x_2, x_3, x_4, x_5, x_6, x_7, y_0, y_1, y_2, y_3, y_4, y_5, y_6, y_7 over Finite Field in a of size 2^8 sage: poly_x = uF(x_0 * X^0 + x_1 * X^1 + x_2 * X^2 + x_3 * X^3 + x_4 * X^4 + x_5 * X^5 + x_6 * X^6 + x_7 * X^7) sage: poly_y = uF(y_0 * X^0 + y_1 * X^1 + y_2 * X^2 + y_3 * X^3 + y_4 * X^4 + y_5 * X^5 + y_6 * X^6 + y_7 * X^7)  (which is very much like I found it in the sources of sage.crypto.mq.rijndael_gf.RijndaelGF) But the coefficients of poly_x and poly_y are not the variables x_0, x_1 etc. but the X^0, X^1, etc... I also tried: sage: F = GF(2^8, 'X') sage: X = F.gen() X sage: x_coeffs = list(var('x_%d' % i) for i in range(8)) sage: y_coeffs = list(var('y_%d' % i) for i in range(8)) sage: poly_x = 0*X sage: type(poly_x) sage: for i in xrange(8): ....: poly_x += x_coeffs[i] * X^i ....: sage: poly_x x_0 + X*x_1 + X^2*x_2 + X^3*x_3 + X^4*x_4 + X^5*x_5 + X^6*x_6 + X^7*x_7 sage: type(poly_x) sage: poly_x.coefficients() [[X*x_1 + X^2*x_2 + X^3*x_3 + X^4*x_4 + X^5*x_5 + X^6*x_6 + X^7*x_7, 0], [1, 1]]  which is also not what I want. Also, expressions like the follow lead to an error: sage: F(x_1*X) TypeError: unable to coerce  How can I express unknown elements with unknown coefficients? 2018-11-05 15:45:40 -0600 received badge ● Student (source) 2018-11-05 15:26:24 -0600 asked a question how to get the transformation matrix for a transformation over 4x4 matrices? I have the following transformation: M = MatrixSpace(QQ,4,4) def f(m): return matrix([ [m, m, m, m], [m, m, m, m], [m, m, m, m], [m, m, m, m] ]) print linear_transformation(M, M, f)  This is not working - but I can't figure out what linear_transformation is expecting. How can I get this to work? Is this even possible?