从Python（ctypes）将多项式发送到PARI / GP [英] Sending a Polynomial to PARI/GP from Python (ctypes)
问题描述
我想调用 x ^ 2-7x + 12 ，这是 gp 可以处理四次多项式的一个非常简单的示例：
I would like to call nfroots({nf}; x) function of PARI/GP from Python. (see function no 3.13.135.on page 371 in this link:), but the probllem is, I couldn't send the algebraic expression or the polynomial, that need to be send, for example, x^2-7x+12, here is a very simple example of what gp can do with a quartic polynomial:
> 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
从答案 Stephan Schlecht（单击此处），我设法写-
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，有创建PARI对象的特定过程（请参见 Stephan Schlecht 的回答） ，我更改了 t_POL = 10 的值，但是代码不起作用，如何从python执行上面的PARI / GP代码？
Note that there is specific process to create of PARI objects (see the answer of Stephan Schlecht), I changed the value for t_POL = 10 , but the code didn't work, How can I execute the above PARI/GP code from python?
推荐答案
一种解决方案可能是：
- 使用gtopoly，返回类型为
POINTER（c_long） - nfroots的返回类型为
POINTER（POINTER（c_long）） - 具有
.pari_printf
- use gtopoly, return type is
POINTER(c_long) - return type of nfroots is
POINTER(POINTER(c_long)) - output of result with
.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
如果您运行该程序，则会得到在调试控制台中所需的输出：
If you run the program you get the desired output in the debug console:
[3, 4]
转化
长度 可以确定向量的长度，请参见
https://pari.math.u-bordeaux.fr/dochtml/html/Conversions_and_like_elementary_functions_or_commands.html#length
With glength one can determine the length of a vector, see
https://pari.math.u-bordeaux.fr/dochtml/html/Conversions_and_similar_elementary_functions_or_commands.html#length
如果参数的类型为t_INT，则使用 itos 可以返回长整数，请参见 https://pari.math.u-bordeaux.fr/pub/pari/manuals/2.7.6/ libpari.pdf 。
With itos a long can be returned if the parameter is of type t_INT, see section 4.4.6 of https://pari.math.u-bordeaux.fr/pub/pari/manuals/2.7.6/libpari.pdf.
在代码中看起来像这样：
In code it would look like this:
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形式。可以这样使用：
To GENtostr gives a string representation of the argument. It could be used like so:
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，请参见上面的两个链接。
There are many more conversion options, see the two links above.
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