A linear system correctly solved symbolically is nots solved when partially specialized with complex constants

[emanuel.c...@gmail.com]

Consider :

from sympy import symbols, Eq, solve, I
L1, L2, L3, L4, C1, C2, C3, C4, M23, I1, I2, I3, I4, U, w, p, RL, J = \
symbols("L1, L2, L3, L4, C1, C2, C3, C4, M23, I1, I2, I3, I4, U, w, p, RL, J")
Sys = [Eq(I1*(J*L1*w - J/(C1*w)) + I2*J/(C1*w), U),
           Eq(I2*(J*L2*w - J/(C2*w) - J/(C1*w)) + I3*(J*M23*w + J/(C2*w)) + I1*J/(C1*w), 0),
           Eq(I2*(J*M23*w + J/(C2*w)) + I3*(J*L3*w - J/(C3*w) - J/(C2*w)) + I4*J/(C3*w), 0),
           Eq(I4*RL + I3*J/(C3*w) - I4*J/(C3*w), 0)]
IVars = [I1, I2, I3, I4]
Sol = solve(Sys, IVars)
Chk = [u.subs(Sol).simplify() for u in Sys]

This system is solved in a matter of milliseconds, and the (unique) solution is correct :

>>> Chk [True, True, True, True]

However, this :

>>> Sys0 = [u.subs({J:I}) for u in Sys]
>>> Sol0 = solve(Sys0, IVars)

“never” returns (i. e. didn’t return after >90 minutes).

WTF ?

​

[Aaron Meurer]

Can you open an issue in the issue tracker for this
https://github.com/sympy/sympy/issues/new. It looks like it is getting
stuck trying to compute polynomial gcds. The issue seems to be
specific to I. If you instead replace J with a real number, it works.
My guess is the fact that it's an algebraic extension causes it to get
stuck in some slow polys algorithm, or possibly an algorithm that is
bugged.

Aaron Meurer

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[emanuel.c...@gmail.com]

Le mercredi 12 octobre 2022 à 01:47:31 UTC+2, asme...@gmail.com a écrit :

Can you open an issue in the issue tracker for this
https://github.com/sympy/sympy/issues/new.

Done.

HTH,