Status: Accepted
Owner: ----
Labels: Type-Defect Priority-Medium
New issue 1629 by ondrej.certik: solve() raises an exception for quartic
equation
http://code.google.com/p/sympy/issues/detail?id=1629
The code below:
from sympy import *
p,q,w,g,f = symbols('pqwgf')
fn = w*((70400*f**2*g**2 - 2592000*g**3 + 12420*g*f**4 + 132*f**6)*cos (p)
+ (70400*f**2*g**2 - 2592000*g**3 + 12420*g*f**4 + 132*f**6)*cos (q) +
(70400*f**2*g**2 - 2592000*g**3 + 12420*g*f**4 + 132*f**6)*cos(p - q) +
(1600*f**2*g**2 - 48000*g**3 + 180*g*f**4 - 12*f**6)*cos(-2*q + 2*p) +
(25600*f**2*g**2 - 224000*g**3 - 360*g*f**4 + 12*f**6)*cos(p + q) +
(25600*f**2*g**2 - 224000*g**3 - 360*g*f**4 + 12*f**6)*cos(p - 2*q) +
(25600*f**2*g**2 - 224000*g**3 - 360*g*f**4 + 12*f**6)*cos(q - 2*p)) +
w**2*((-800*g**2 - 180*g*f**2 + 18*f**4)*cos(-2*q + 2*p) + (-35200*g**2 -
12420*g*f**2 - 198*f**4)*cos(p) + (-35200*g**2 - 12420*g*f**2 -
198*f**4)*cos(q) + (-35200*g**2 - 12420*g*f**2 - 198*f**4)*cos(p - q) +
(-12800*g**2 + 360*g*f**2 - 18*f**4)*cos(p + q) + (-12800*g**2 + 360*g*f**2
- 18*f**4)*cos(p - 2*q) + (-12800*g**2 + 360*g*f**2 - 18*f**4)*cos(q -
2*p)) + w**3*((-120*g + 12*f**2)*cos(p + q) + (-120*g + 12*f**2)*cos(p -
2*q) + (-120*g + 12*f**2)*cos(q - 2*p) + (60*g - 12*f**2)*cos(-2*q + 2*p) +
(4140*g + 132*f**2)*cos(p) + (4140*g + 132*f**2)*cos(q) + (4140*g +
132*f**2)*cos(p - q)) + w**4* (-33*cos(p) - 33*cos(q) - 33*cos(p - q) -
3*cos(p + q) - 3*cos(p - 2*q) - 3*cos(q - 2*p) + 3*cos(-2*q + 2*p)) +
(-35200*f**4*g**2 + 2592000*f**2*g**3 - 47360000*g**4 - 4140*g*f**6 -
33*f**8)*cos(p) + (-35200*f**4*g**2 + 2592000*f**2*g**3 - 47360000*g**4 -
4140*g*f**6 - 33*f**8)*cos(q) + (-35200*f**4*g**2 + 2592000*f**2*g**3 -
47360000*g**4 - 4140*g*f**6 - 33*f**8)*cos(p - q) + (-12800*f**4*g**2 +
224000*f**2*g**3 - 3840000*g**4 + 120*g*f**6 - 3*f**8)*cos(p + q) +
(-12800*f**4*g**2 + 224000*f**2*g**3 - 3840000*g**4 + 120*g*f**6 -
3*f**8)*cos(p - 2*q) + (-12800*f**4*g**2 + 224000*f**2*g**3 - 3840000*g**4
+ 120*g*f**6 - 3*f**8)*cos(q - 2*p) + (-800*f**4*g**2 + 48000*f**2*g**3 -
640000*g**4 - 60*g*f**6 + 3*f**8)*cos(-2*q + 2*p)
print solve(fn,w)
produces:
Traceback (most recent call last):
File "q.py", line 4, in <module>
print solve(fn,w)
File "/home/ondrej/repos/sympy/sympy/solvers/solvers.py", line 207, in
solve
result = roots(poly, cubics=True, quartics=True).keys()
File "/home/ondrej/repos/sympy/sympy/polys/rootfinding.py", line 291, in
roots
_, factors = poly_factors(f)
File "/home/ondrej/repos/sympy/sympy/polys/factortools.py", line 36, in
poly_factors
F = Poly(f, *symbols)
File "/home/ondrej/repos/sympy/sympy/polys/polynomial.py", line 389, in
__new__
terms = Poly._decompose(poly.as_basic(), *symbols)
File "/home/ondrej/repos/sympy/sympy/polys/polynomial.py", line 545, in
_decompose
raise PolynomialError("Can't decompose %s" % factor)
sympy.polys.polynomial.PolynomialError: Can't decompose cos(q - p)
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