如何在python中解决全等系统? [英] How to solve a congruence system in python?
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问题描述
对于问题Ax≡B(MOD C),我做到了,没关系:
for the problem Ax ≡ B (MOD C) I did this, and it was okay:
def congru(a,b,c):
for i in range(0,c):
if ((a*i - b)%c)== 0 :
print(i)
现在我必须解决一个方程组,其中A =(5x + 7y)和A =(6x + 2y), B分别为4和B = 12,C为26.
Now I have to solve a system of equations, where A = ( 5x + 7y) and A= (6x + 2y), and B= 4 and B = 12 , respectively, and C is 26.
换句话说: (5x + 7y)≡4(mod 26) (6x + 2y)≡12(mod 26)
In other words: ( 5x + 7y)≡ 4 (mod 26) (6x + 2y)≡ 12 (mod 26)
我该怎么做?
谢谢.
推荐答案
这是一个非常快速的线性同余求解器,可以在一秒钟内解决4096个字节数.递归版本在此长度上达到其最大深度:
This is a very fast linear congruence solver that can solve a 4096 byte number in a second. Recursion versions meet their max depth at this length:
#included if you use withstats=True, not needed otherwise
def ltrailing(N):
return len(str(bin(N))) - len(str(bin(N)).rstrip('0'))
#included if you use withstats=True, not needed otherwise
def _testx(n, b, withstats=False):
s = ltrailing(n - 1)
t = n >> s
if b == 1 or b == n - 1:
return True
else:
for j in range(0, s):
b = pow_mod(b, 2, n, withstats)
if b == n - 1:
return True
if b == 1:
return False
if withstats == True:
print(f"{n}, {b}, {s}, {t}, {j}")
if withstats == True:
print(f"{n}, {b}, {s}, {t}")
return False
def fastlinearcongruence(powx, divmodx, N, withstats=False):
x, y, z = egcditer(powx, N, withstats)
answer = (y*divmodx)%N
if withstats == True:
print(f"answer = {answer}, mrbt = {a}, mrst = {b}, mranswer = {_testx(N, answer)}")
if x > 1:
powx//=x
divmodx//=x
N//=x
if withstats == True:
print(f"powx = {powx}, divmodx = {divmodx}, N = {N}")
x, y, z = egcditer(powx, N, withstats)
if withstats == True:
print(f"x = {x}, y = {y}, z = {z}")
answer = (y*divmodx)%N
if withstats == True:
print(f"answer = {answer}, mrbt = {a}, mrst = {b}, mranswer = {_testx(N, answer)}")
answer = (y*divmodx)%N
if withstats == True:
print(f"answer = {answer}, mrbt = {a}, mrst = {b}, mranswer = {_testx(N, answer)}")
return answer
def egcditer(a, b, withstats=False):
s = 0
r = b
old_s = 1
old_r = a
quotient = 0
if withstats == True:
print(f"quotient = {quotient}, old_r = {old_r}, r = {r}, old_s = {old_s}, s = {s}")
while r!= 0:
quotient = old_r // r
old_r, r = r, old_r - quotient * r
old_s, s = s, old_s - quotient * s
if withstats == True:
print(f"quotient = {quotient}, old_r = {old_r}, r = {r}, old_s = {old_s}, s = {s}")
if b != 0:
bezout_t = quotient = (old_r - old_s * a) // b
if withstats == True:
print(f"bezout_t = {bezout_t}")
else:
bezout_t = 0
if withstats == True:
print("Bézout coefficients:", (old_s, bezout_t))
print("greatest common divisor:", old_r)
return old_r, old_s, bezout_t
要使用:
In [2703]: fastlinearcongruence(63,1,1009)
Out[2703]: 993
In [2705]: fastlinearcongruence(993,1,1009)
Out[2705]: 63
Also this is 100x faster than pow when performing this pow:
pow(1009, 2**bit_length()-1, 2**bit_length())
where the answer is 273.
This is equivalent to the much faster:
In [2713]: fastlinearcongruence(1009,1,1024)
Out[2713]: 273
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