将多项式从 Python 发送到 PARI/GP (ctypes)

Question

我想调用PARI/GP from Python. (see function no 3.13.135.on page 371 in this link:)的nfroots({nf}; x)函数，但问题是，我无法发送需要发送的代数表达式或多项式，例如，x^2-7x+12，这是一个非常简单的例子，说明 gp 可以用四次多项式做什么：

> V = readvec("coeff.txt");
> print(V)
[1,-7,12]
> P = Pol(V);  # I get following error when I use Pol in my code:    func=self._FuncPtr((name_or_ordinal, self)) AttributeError: function 'pol' not found 
> print(P)
x^2 -7*x +12
> print(nfroots(,P))
>4, 3

根据的回答，我设法写了 -

from ctypes import *
pari = cdll.LoadLibrary("C:\Program Files\Pari64-2-11-3\libpari.dll")

pari.stoi.restype = POINTER(c_long)
pari.cgetg.restype = POINTER(POINTER(c_long))

pari.nfroots.restype = POINTER(POINTER(c_long))


pari.pari_init(2 ** 19, 0)

def t_vec(numbers):
    l = len(numbers) + 1
    p1 = pari.cgetg(c_long(l), c_long(10)) #t_POL    =  10,
    for i in range(1, l):
        p1[i] = pari.stoi(c_long(numbers[i - 1]))
    return p1

def main():    
    h = "x^2-7x+12"
    res = pari.nfroots(t_vec(h))  
for i in range(1, len(res)):
         print(pari.itos(res[i]))
if __name__ == '__main__':
    main()

请注意，创建 PARI 对象有特定的过程（请参阅的答案），我更改了 t_POL = 10 的值，但代码不起作用，我怎么能从 python?

执行上面的 PARI/GP 代码

Answer 1

一个解决方案可能是：

使用gtopoly，return类型是POINTER(c_long)
return nfroots 的类型是 POINTER(POINTER(c_long))
.pari_printf

代码

from ctypes import *

pari = cdll.LoadLibrary("libpari.so")

pari.stoi.restype = POINTER(c_long)
pari.cgetg.restype = POINTER(POINTER(c_long))
pari.gtopoly.restype = POINTER(c_long)
pari.nfroots.restype = POINTER(POINTER(c_long))

(t_VEC, t_COL, t_MAT) = (17, 18, 19)  # incomplete
precision = c_long(38)

pari.pari_init(2 ** 19, 0)


def t_vec(numbers):
    l = len(numbers) + 1
    p1 = pari.cgetg(c_long(l), c_long(t_VEC))
    for i in range(1, l):
        p1[i] = pari.stoi(c_long(numbers[i - 1]))
    return p1


def main():
    V = (1, -7, 12)
    P = pari.gtopoly(t_vec(V), c_long(-1))
    res = pari.nfroots(None, P)
    pari.pari_printf(bytes("%Ps\n", "utf8"), res)


if __name__ == '__main__':
    main()

测试

如果您运行程序，您将在调试控制台中获得所需的输出：

[3, 4]

转化次数

用glength可以确定向量的长度，见 https://pari.math.u-bordeaux.fr/dochtml/html/Conversions_and_similar_elementary_functions_or_commands.html#length

使用 itos 如果参数的类型为 t_INT，则 long 可以 returned，请参阅 https://pari.math.u-bordeaux.fr/pub/pari/manuals/2.7.6/libpari.pdf 的第 4.4.6 节。

在代码中它看起来像这样：

pari.glength.restype = c_long
pari.itos.restype = c_long
... 
print("elements as long (only if of type t_INT): ")
for i in range(1, pari.glength(res) + 1):
    print(pari.itos(res[i]))

To GENtostr 给出参数的字符串表示。它可以像这样使用：

pari.GENtostr.restype = c_char_p
...
print("elements as generic strings: ")
for i in range(1, pari.glength(res) + 1):
    print(pari.GENtostr(res[i]).decode("utf-8"))

还有更多转换选项，请参阅上面的两个链接。

将多项式从 Python 发送到 PARI/GP (ctypes)

Sending a Polynomial to PARI/GP from Python (ctypes)

python

ctypes

pari

python-3.x