__getitem__ followed by idealfrobenius -> SystemError

[pjbruin]

In cypari2 2.1.3, the code

from cypari2.pari_instance import Pari
pari = Pari()
M = pari('nfinit(x^2 + 1)')
P = M.idealfactor(7)[0, 0]
G = M.galoisinit()
print(G[5])  # error does not arise without this line
print(M.idealfrobenius(G, P))

raises SystemError: new_gen() argument not on PARI stack, not on PARI heap and not a universal constant

Possibly related: #133

[pjbruin]

Here is the output of G.debug() before doing G[5]:

[&=00007fa27bfff808] VEC(lg=9):2200000000000009 00007fa27bfff7e0 00007fa27bfff790 00007fa27bfff730 00007fa27bfff6e8 00007fa27bfff640 00007fa27bfff628 00007fa27bfff5e8 00007fa27bfff5c0 
  1st component = [&=00007fa27bfff7e0] POL(lg=5):1400000000000005 (+,varn=0):4000000000000000 00007fa27bfff7c8 00007fa28166a900 00007fa27bfff7b0 
    coef of degree 0 = [&=00007fa27bfff7c8] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000001 
    coef of degree 1 = gen_0
    coef of degree 2 = [&=00007fa27bfff7b0] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000001 
  2nd component = [&=00007fa27bfff790] VEC(lg=4):2200000000000004 00007fa27bfff778 00007fa27bfff760 00007fa27bfff748 
    1st component = [&=00007fa27bfff778] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 000000000000000d 
    2nd component = [&=00007fa27bfff760] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000002 
    3rd component = [&=00007fa27bfff748] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 00000000000000a9 
  3rd component = [&=00007fa27bfff730] VEC(lg=3):2200000000000003 00007fa27bfff718 00007fa27bfff700 
    1st component = [&=00007fa27bfff718] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000063 
    2nd component = [&=00007fa27bfff700] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000046 
  4th component = [&=00007fa27bfff6e8] MAT(lg=3):2600000000000003 00007fa27bfff6d0 00007fa27bfff688 
    mat(1,1) = [&=00007fa27bfff6b8] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000055 
    mat(1,2) = [&=00007fa27bfff670] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000055 
    mat(2,1) = [&=00007fa27bfff6a0] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000023 
    mat(2,2) = [&=00007fa27bfff658] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000086 
  5th component = [&=00007fa27bfff640] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000001 
  6th component = [&=00007fa27bfff628] VEC(lg=3):2200000000000003 00007fa27bfff610 00007fa27bfff5f8 
    1st component = [&=00007fa27bfff610] VECSMALL(lg=3):2c00000000000003 0000000000000001 0000000000000002 
    2nd component = [&=00007fa27bfff5f8] VECSMALL(lg=3):2c00000000000003 0000000000000002 0000000000000001 
  7th component = [&=00007fa27bfff5e8] VEC(lg=2):2200000000000002 00007fa27bfff5d0 
    1st component = [&=00007fa27bfff5d0] VECSMALL(lg=3):2c00000000000003 0000000000000002 0000000000000001 
  8th component = [&=00007fa27bfff5c0] VECSMALL(lg=2):2c00000000000002 0000000000000002 

After doing G[5]:

[&=000056555531dcc0] VEC(lg=9,CLONE):2300000000000009 000056555531df28 000056555531ded8 000056555531de78 000056555531de30 000056555531dd88 000056555531dd70 000056555531dd30 000056555531dd08 
  1st component = [&=000056555531df28] POL(lg=5):1400000000000005 (+,varn=0):4000000000000000 000056555531df10 00007fa28166a900 000056555531def8 
    coef of degree 0 = [&=000056555531df10] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000001 
    coef of degree 1 = gen_0
    coef of degree 2 = [&=000056555531def8] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000001 
  2nd component = [&=000056555531ded8] VEC(lg=4):2200000000000004 000056555531dec0 000056555531dea8 000056555531de90 
    1st component = [&=000056555531dec0] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 000000000000000d 
    2nd component = [&=000056555531dea8] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000002 
    3rd component = [&=000056555531de90] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 00000000000000a9 
  3rd component = [&=000056555531de78] VEC(lg=3):2200000000000003 000056555531de60 000056555531de48 
    1st component = [&=000056555531de60] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000063 
    2nd component = [&=000056555531de48] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000046 
  4th component = [&=000056555531de30] MAT(lg=3):2600000000000003 000056555531de18 000056555531ddd0 
    mat(1,1) = [&=000056555531de00] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000055 
    mat(1,2) = [&=000056555531ddb8] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000055 
    mat(2,1) = [&=000056555531dde8] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000023 
    mat(2,2) = [&=000056555531dda0] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000086 
  5th component = [&=000056555531dd88] INT(lg=3):0200000000000003 (+,lgefint=3):4000000000000003 0000000000000001 
  6th component = [&=000056555531dd70] VEC(lg=3):2200000000000003 000056555531dd58 000056555531dd40 
    1st component = [&=000056555531dd58] VECSMALL(lg=3):2c00000000000003 0000000000000001 0000000000000002 
    2nd component = [&=000056555531dd40] VECSMALL(lg=3):2c00000000000003 0000000000000002 0000000000000001 
  7th component = [&=000056555531dd30] VEC(lg=2):2200000000000002 000056555531dd18 
    1st component = [&=000056555531dd18] VECSMALL(lg=3):2c00000000000003 0000000000000002 0000000000000001 
  8th component = [&=000056555531dd08] VECSMALL(lg=2):2c00000000000002 0000000000000002 

[videlec]

Could you test with #134?

[pjbruin]

#134 does not appear to fix the problem. The function idealfrobenius behaves a bit like a member function: it returns (or at least may return), without copying onto the stack, a component of another GEN, in this case of the list of all elements of the Galois group. However, its prototype is simply GGG.

[videlec]

I see, it is rather the __getitem__ which is problematic.