Consider the following code snippet:
# FACTORIZATION IN F_q[x]
def my_mul(x,y):
if x == None: return y
if y == None: return x
return x*y
# Squarefree Decomposition in F_q[x]
def squarefree_decomposition(GF, f):
p = GF.characteristic()
# base case
if f == 1: return [1]
# recursive case
df = f.diff()
i_factors = [1]
g = gcd(f,df)
w = GF(f / g) #0j0 esto puede promocionar a racional si te descuidas
# collect squarefree factors such that p !| i
while(w != 1):
w_aux = gcd(g,w)
g = GF(g / w_aux)
i_factor = GF(w / w_aux)
i_factors.append(i_factor)
w = w_aux
# here, g = prod[f_(j)^j for p | j]
# collect squarefree factors such that p | j
g_root = GF(g.coefficients(sparse=False)[::p]) # pth root of g
g_root_decomposition = squarefree_decomposition(GF, g_root)
j_factors = [g_root_decomposition[i/p] if i%p==0 else 1 for i in xrange(p*(len(g_root_decomposition)-1)+1)]
# combine results
res = map(my_mul, i_factors, j_factors)
return res
# Example in F_q[x]
GF125X = GF(5^3)[x]
f = GF125X((x^5 + x^2 + x^1 + 1)^2*x^5)
decom = squarefree_decomposition(GF125X, f)
print("{} decomposes as {}".format(f, decom))
recom = [f_i^i for f_i,i in enumerate(decom)]
recom
When I execute this, I get the following output:
x^15 + 2*x^12 + 2*x^11 + 2*x^10 + x^9 + 2*x^8 + 3*x^7 + 2*x^6 + x^5 decomposes as [1, 1, x^5 + x^2 + x + 1, 1, 1, x]
Error in lines 28-28
Traceback (most recent call last):
File "/cocalc/lib/python2.7/site-packages/smc_sagews/sage_server.py", line 1188, in execute
flags=compile_flags) in namespace, locals
File "", line 1, in <module>
File "sage/rings/polynomial/polynomial_template.pxi", line 605, in sage.rings.polynomial.polynomial_zz_pex.Polynomial_template.__pow__ (build/cythonized/sage/rings/polynomial/polynomial_zz_pex.cpp:12318)
raise NotImplementedError("%s^%s not defined."%(ee,self))
NotImplementedError: 1^1 not defined.
I notice I am confused. AFAIK, there is only one sensible result for 1^1, namely 1. Why do I get this error?
If I try creating a 1 polynomial in a finite field and taking its 1th power it works:
id_ = GF125X(1)
id_^1
Produces as output 1, as expected.
