Le jeudi 11 janvier 2018 03:39:04 UTC+1, Bernat Bassols a écrit :
>
> Hello,
> I have come across an error while solving a (relatively) easy
> trigonometric equation.
> Basically, CoCalc is giving me a solution to an equation that is not
> right.
> Take a look here:
>
> Also the CoCalc Worksheet URL:
> https://cocalc.com/projects/906013bd-a0e4-4ba2-92b9-1d51e7ccb16d/files/2018-01-10-171011.sagews?session=default
>
>
Hmmm... Let's see :
sage: eq=-cos(m)^4*e^(3*m)-2*cos(m)^2*sin(m)^2*e^(3*m)-e^(3*m)*sin(m)^4
sage: eq.solve(m)
[m == 1/2*pi]
Let's check :
sage: eq=-cos(m)^4*e^(3*m)-2*cos(m)^2*sin(m)^2*e^(3*m)-e^(3*m)*sin(m)^4
sage: S1=eq.solve(m);S1
[m == 1/2*pi]
Let's check :
sage: eq.subs(S1)
-e^(3/2*pi)
Nice failure... But :
sage: S2=eq.solve(m,to_poly_solve='force');S2
[]
Looks better. By the way :
sage: eq.factor().trig_reduce()
-e^(3*m)
which has no solution.
How well fares "the competition" ?
sage: import sympy
sage: sympy.solve(eq,m)
[]
sage: from giacpy_sage import *
sage: libgiac.solve(eq,m)
Warning, argument is not an equation, solving
-cos(m)^4*exp(m*3)-cos(m)^2*exp(m*3)*sin(m)^2*2-exp(m*3)*sin(m)^4=0
[]
sage: fricas.solve(eq,m)
[]
sage: maple.solve(eq==0,m)
sage: mathematica.Solve(eq==0,m)
{}
Maple's answer is dubious (I might have a wrong syntax). The rest of the
bunch correctly solves the problem ; so the problem is with Maxima's
default algorithm.
Is there anything that can be done to solve this issue?
>
- Check your results (always useful with CASes (any of them)).
- Use alternate systems (see above).
- File a ticket against Maxima... Unless you do this, I'll do it
(probably this week-end).
> Thank you in advance.
>
You're welcome.
--
Emmanuel Charpentier
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