On Tue, Nov 18, 2025 at 3:09 AM [email protected] <[email protected]>
wrote:
> yes in fact the initial value should be bigger, then there are no
> singularities, but even then I get
>
> --------------------------------------------------------------------------
> RuntimeError Traceback (most recent call last)
> /usr/lib/python3/dist-packages/sage/calculus/ode.pyx in
> sage.calculus.ode.ode_solver.ode_solve
> (build/cythonized/sage/calculus/ode.c:6834)() 554 if (status !=
> GSL_SUCCESS): --> 555 raise RuntimeError 556 except RuntimeError:
> RuntimeError: During handling of the above exception, another exception
> occurred: ValueError Traceback (most recent call last)
> /tmp/ipykernel_125/2547832258.py in <module> ----> 1 ra.ode_solve(y_0=[
> RealNumber('3.1')],t_span=[Integer(0),Integer(1)],num_points=Integer(1000)
> ) /usr/lib/python3/dist-packages/sage/calculus/ode.pyx in
> sage.calculus.ode.ode_solver.ode_solve
> (build/cythonized/sage/calculus/ode.c:6934)() 560 sig_free(y) 561 sig_free
> (scale_abs_array) --> 562 raise ValueError("error solving") 563 564 for j
> from 0<=j<dim: ValueError: error solving
>
> But now I realize that my version is quite old: 'SageMath version 9.5,
> Release Date: 2022-01-30' Perhaps that's why it doesn't work?
>
in the current beta, SageMath 10.8.beta9, the following works:
sage: t,y=var('t,y');
....: g= lambda t,y:[-y[0]/(2*y[0]**3 - 1)];
....: ra = ode_solver();
....: ra.function=g;
....: ra.ode_solve(y_0=[1.5],t_span=[0,1], num_points=1000)
(the values of y_0 between [1.0] and [1.4] lead to a hang)
This is a gsl ODE backend.
> In fact the following works: t,y=var('t,y')
> numsol=desolve_rk4( -y/(2*y^3 - 1), dvar=y, ivar=t,
> ics=[0,2.1],end_points=1, step=0.001)
> kuva=line(numsol,axes_labels=[t,y])
> kuva.show()
>
This is a different ODE solver backend, a Maxima one
HTH
Dima
> maanantai 17. marraskuuta 2025 klo 19.52.18 UTC+2 [email protected]
> kirjoitti:
>
>> even for the 1st order ODE, y must be a vector.
>> (and, apparently, for y as well)
>>
>> The following example works:
>>
>> sage: t,y=var('t,y');
>> ....: g= lambda t,y:[-y[0]]; # ODE y'=-y
>> ....: ra = ode_solver();
>> ....: ra.function=g;
>> ....: ra.ode_solve(y_0=[1],t_span=[0,1],num_points=100)
>>
>> Now, if I change g to
>>
>> g= lambda t,y:[-y[0]/(2*y[0]^3 - 1)];
>>
>> the example runs, but seemingly never stops. Perhaps you hit a
>> singularity somewhere that results in
>> such a non-convergence.
>>
>> On Monday, November 17, 2025 at 10:21:42 AM UTC-6 Dima Pasechnik wrote:
>>
>>> On Mon, Nov 17, 2025 at 3:45 AM [email protected] <[email protected]>
>>> wrote:
>>>
>>>> According to the manual the following should work:
>>>>
>>>> t,y=var('t,y');
>>>> g= lambda t,y:-y/(2*y^3 - 1);
>>>> ra = ode_solver();
>>>> ra.function=g;
>>>> ra.ode_solve(y_0=1,t_span=[0,1],num_points=100)
>>>>
>>>
>>>
>>> Please write the ODE you want to solve, in the usual maths notation -
>>> it's not clear what it is.
>>>
>>>
>>>
>>>>
>>>> However, I get the error message
>>>>
>>>>
>>>> ---------------------------------------------------------------------------
>>>> TypeError Traceback (most recent call last)
>>>> /tmp/ipykernel_317/557462051.py in <module> ----> 1 ra.ode_solve(y_0=
>>>> Integer(1),t_span=[Integer(0),Integer(1)],num_points=Integer(100))
>>>> /usr/lib/python3/dist-packages/sage/calculus/ode.pyx in
>>>> sage.calculus.ode.ode_solver.ode_solve
>>>> (build/cythonized/sage/calculus/ode.c:5124)() 412 self.y_0 = y_0 413 -->
>>>> 414 dim = len(self.y_0) 415 type = isinstance(self.function,ode_system)
>>>> 416 if type == 0: TypeError: object of type
>>>> 'sage.rings.integer.Integer' has no len()
>>>>
>>>> Also
>>>> def f(t,y): return -y/(2*y^3 - 1);
>>>> ra.function=f;
>>>>
>>>> gives the same error.
>>>>
>>>> ??
>>>>
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>>>>
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