On Thursday, July 26, 2012 6:37:56 AM UTC-4, Nasser M. Abbasi wrote:
>
> I do not know much of anything about sage. But I was using desolve on
> http://www.sagenb.org to compare an answer,
>
Tata! You clearly know *something* about it, or you wouldn't have done as
well as you have finding stuff out.
When I ask sage to solve an ode using desolve, it seems to use `c` for
> constant of integration in the result, like this:
>
>
Yes, we get this directly from Maxima, except (I believe) as %c.
> reset()
> x= var('x')
> y = function('y', x)
> desolve(diff(y,x)+y, y,ivar=x)
>
> which gives
>
> c*e^(-x)
>
> I wish it generated at least uppercase `C` or such. But any way. Now the
> confusing part.
>
>
Actually, it's worse than that.
c
Traceback (click to the left of this block for traceback)
...
NameError: name 'c' is not defined
So as you can see, this "c" from Maxima is not really "there" in the same
sense. Interestingly, Sage still knows it's there and a symbolic
expression (the "c", I mean), but it's purely local in some sense that I
don't quite get.
> If I use `c` myself in the ode, then the result will contains 2 c's. The
> constant of integration `c` that sage uses, and my own `c` which I have in
> the ode itself. So how is a user to know which is which when they look at
> the result??
>
>
Right, this is a problem.
> Is there a way to tell sage to use at least upper case letter for constant of
> integration?
>
>
I don't think that would make any difference. Then people who like
defining upper-case variables would get upset. The real problem is that
some conflict should be detected and this variable replaced by something -
but what? I could imagine someone already having defined c, c1, c2, c3, C,
C1, C2, C3, c_1, C_1, etc. - now what should Sage pick? It's not obvious.
Anyway, this has been noticed in the past -
see http://trac.sagemath.org/sage_trac/ticket/9421 for where we are
tracking this. http://trac.sagemath.org/sage_trac/ticket/6882 should in
theory solve this, but first we would need to find a way to do that in a
user-friendly way.
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