How to tell sympy dsolve not to solve the ode using series?

[nma%12...@gtempaccount.com]

I am learning sympy dsolve. I find that it sometimes solve the ode using series when not asked to do this.

I know dsolve has hints to ask it to solve using series.

Is there a way to tell dsolve not to use series solution if it can't solve the ode using exact methods?

Here is an example. Using sympy 1.13.1

-----------------------------------

>python
Python 3.13.1 (main, Dec 4 2024, 18:05:56) [GCC 14.2.1 20240910] on linux
Type "help", "copyright", "credits" or "license" for more information.

 
from sympy import *
x = symbols("x")
y = Function("y")
ode = Eq(x*(1 - x)*Derivative(y(x), x) + y(x)*exp(x) + Derivative(y(x), (x, 2)),0)
ics = {}
dsolve(ode,func=y(x),ics=ics)

It gives

  

Eq(y(x), C2*(x**4*exp(2*x)/24 + x**4*exp(x)/12 - x**2*exp(x)/2 + 1) + C1*x*(x**3/12 - x**2*exp(x)/6 - x**2/6 + 1) + O(x**6))

You see, the solution is series solution as it has O(...) at the end even though there is no hint to use series in the command.

Is it possible to do this?

--Nasser

[nma%12...@gtempaccount.com]

Fyi, there was a bug report on this same issue 6 years ago

https://github.com/sympy/sympy/issues/15916 

But it is still not fixed?   I also tried 

dsolve(ode,func=y(x),ics=ics,series=False)

And it still returned series solution. This is wrong. It should only return series solution when explicitly asked to.

--Nasser

[Aaron Meurer]

Yes, this is a known issue. It shouldn't be too difficult to fix, it
just hasn't been done yet.

However, series is currently the last thing that is attempted. So if
you get a series solution, it really means it just doesn't know how to
solve the ode. You can also check this using classify_ode:

>>> classify_ode(ode)
('factorable', '2nd_power_series_ordinary')

"factorable" is a meta-hint that appears for every ODE. And the only
other one is series. So no algorithms are implemented that can solve
this ODE.

Aaron Meurer

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[peter.st...@gmail.com]

Dear Aaron,

maybe a dumb question from a retired engineer:
'Most' ODEs cannot be solved in closed form anyway - or so I recall.
What is the point of trying to solve symbolically the 'few' that can be solved in closed form?

Thanks,

Peter

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