Re: [Maxima-discuss] bug in ic1

[Dimiter P. <dim...@gm...>]

Hi Robert,

The issue arose in multiple indefinite integration,
which I then converted programmatically to definite integrals
So I think that if ic1 is changed to signature
ic(z(x)=%c-expr(x),x=x0,z(x)=0, [%c])

the problem will be solved.

best regards,

Dimiter

On Sat, Feb 27, 2021 at 5:41 PM Robert Dodier <rob...@gm...>
wrote:

> On Sun, Feb 21, 2021 at 11:34 AM Dimiter Prodanov <dim...@gm...>
> wrote:
>
> > ic1(z(x)=%c1-'integrate((z(u607)^2*(x-u607))/u607,u607,x,M),x=M,z(x)=0);
> > crashes
>
> > however
> > ic1(z(x)=%c-'integrate((z(u607)^2*(x-u607))/u607,u607,x,M),x=M,z(x)=0);
> >
> > returns
> > z(x)=z(M)-integrate((z(u607)^2*x-u607*z(u607)^2)/u607,u607,x,M)
> >
> > So in my view, the symbol %c should not be hardcoded in ic1.
>
> Hi Dimiter, by the way, from where did %c1 appear?
>
> I've looked at this problem for a bit, and what I'm seeing is that the
> ode2 code assumes throughout that constants are only named %c, %k1, or
> %k2. It wouldn't be too hard to change that to numbered constants;
> there is already a mechanism (integration_constant and
> integration_constant_counter) to generate numbered constants in the
> integration code.
>
> There are at least two problems introduced by that. The smaller one is
> that the presence of numbered constants would probably make it harder
> to check results automatically. OK, that can be fixed up without much
> trouble.
>
> The larger one is that the results might seem messy to users. After a
> while you'll get stuff like %k67*sin(x) + %k68*cos(x) and if you want
> "nice" constants you'll have to reset integration_constant_counter.
> That sounds painful.
>
> In some sense creating new constants is the right thing to do. Is it
> sufficiently right to overcome the clumsiness of it? What does anyone
> think about any of this stuff?
>
> best,
>
> Robert Dodier
>