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-# module 'zmod'
-
-# Compute properties of mathematical "fields" formed by taking
-# Z/n (the whole numbers modulo some whole number n) and an
-# irreducible polynomial (i.e., a polynomial with only complex zeros),
-# e.g., Z/5 and X**2 + 2.
-#
-# The field is formed by taking all possible linear combinations of
-# a set of d base vectors (where d is the degree of the polynomial).
-#
-# Note that this procedure doesn't yield a field for all combinations
-# of n and p: it may well be that some numbers have more than one
-# inverse and others have none. This is what we check.
-#
-# Remember that a field is a ring where each element has an inverse.
-# A ring has commutative addition and multiplication, a zero and a one:
-# 0*x = x*0 = 0, 0+x = x+0 = x, 1*x = x*1 = x. Also, the distributive
-# property holds: a*(b+c) = a*b + b*c.
-# (XXX I forget if this is an axiom or follows from the rules.)
-
-import poly
-
-
-# Example N and polynomial
-
-N = 5
-P = poly.plus(poly.one(0, 2), poly.one(2, 1)) # 2 + x**2
-
-
-# Return x modulo y. Returns >= 0 even if x < 0.
-
-def mod(x, y):
- return divmod(x, y)[1]
-
-
-# Normalize a polynomial modulo n and modulo p.
-
-def norm(a, n, p):
- a = poly.modulo(a, p)
- a = a[:]
- for i in range(len(a)): a[i] = mod(a[i], n)
- a = poly.normalize(a)
- return a
-
-
-# Make a list of all n^d elements of the proposed field.
-
-def make_all(mat):
- all = []
- for row in mat:
- for a in row:
- all.append(a)
- return all
-
-def make_elements(n, d):
- if d == 0: return [poly.one(0, 0)]
- sub = make_elements(n, d-1)
- all = []
- for a in sub:
- for i in range(n):
- all.append(poly.plus(a, poly.one(d-1, i)))
- return all
-
-def make_inv(all, n, p):
- x = poly.one(1, 1)
- inv = []
- for a in all:
- inv.append(norm(poly.times(a, x), n, p))
- return inv
-
-def checkfield(n, p):
- all = make_elements(n, len(p)-1)
- inv = make_inv(all, n, p)
- all1 = all[:]
- inv1 = inv[:]
- all1.sort()
- inv1.sort()
- if all1 == inv1: print 'BINGO!'
- else:
- print 'Sorry:', n, p
- print all
- print inv
-
-def rj(s, width):
- if type(s) is not type(''): s = `s`
- n = len(s)
- if n >= width: return s
- return ' '*(width - n) + s
-
-def lj(s, width):
- if type(s) is not type(''): s = `s`
- n = len(s)
- if n >= width: return s
- return s + ' '*(width - n)