#7560: len(t_span) > 2 case creates len(t_span) - 1 solutions
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Reporter: adavid | Owner: jkantor
Type: defect | Status: needs_work
Priority: minor | Milestone: sage-5.6
Component: numerical | Resolution:
Keywords: ode_solver, ode_solve, t_span | Work issues:
Report Upstream: N/A | Reviewers:
Authors: Jan Medlock | Merged in:
Dependencies: | Stopgaps:
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Comment (by medlock):
Replying to [comment:8 tkluck]:
> This is a very clear explanation in the doctext, thanks.
>
> This part is not entirely right, though:
> {{{
> * If ``t_span`` is a tuple with more than 2 values, then (...)
>
> * If ``t_span`` is a tuple with just 2 time values, then (...) the
user must also specify
> ``num_points``.
> }}}
>
> In the code, the distinction is made based on whether `num_points` is
specified, and not based on the length of `t_span`. That's a good thing.
(remember how your matlab code always breaks when you pass 1x1 matrices to
your generic code for NxN matrices.)
I'm not sure I understand what you're saying. I believe what I've written
is exactly correct. The code in question is:
{{{
if len(self.t_span)==2 and num_points!=False:
# Solve at num_points time steps.
elif len(self.t_span) > 2:
# Solve using t_span as the times.
}}}
http://trac.sagemath.org/sage_trac/browser/sage/gsl/ode.pyx#L495
&
http://trac.sagemath.org/sage_trac/browser/sage/gsl/ode.pyx#L538
I agree that it is not ideal: the second condition should be
`len(self.t_span) >= 2` and there should be an `else` clause to catch mis-
specified `self.t_span`. As for what to do if `len(self.t_span) > 2` and
`num_points` is defined, I think the best thing to do is to use the values
in `self.t_span` and ignore `num_points`. I will put together a patch
with this addition.
> I would also be tempted to change the name of the parameter `num_points`
to `num_intervals`, raising a `DeprecationWarning` for `num_points`. How
do you feel about that?
I personally find points more natural than intervals in this setting.
(You're obviously right that intervals doesn't have the +1 issue.)
--
Ticket URL: <http://trac.sagemath.org/sage_trac/ticket/7560#comment:9>
Sage <http://www.sagemath.org>
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