Personally I don't see how
As a guess, for a substitution like you want to work, the following
much simpler computation
sage: t = var('t')
sage: x = function('x', t)
sage: y = function('y', x)
sage: diff(y,t)
diff(y(x(t)), t, 1)
should yield not diff(y(x(t)), t, 1) but perhaps something like
diff(y(x), x, 1)*diff(x(t),t) ?
I wonder what others think.
On Mon, Dec 8, 2008 at 6:16 PM, bsdz <[EMAIL PROTECTED]> wrote:
>
> Hi
>
> I was wondering if it is possible in Sage (perhaps even Maxima) to
> change the variable in an ODE or PDE algebraically. I have set up a
> simple PDE with the following: -
>
> x, t, k_1, k_2 = var("x t k_1 k_2")
> y = function('y', x, t)
> PDE = lambda f : k_1 * x^2 * diff(f,x,2) + diff(f,t) + k_2*(x*diff(f,x)-f)
> PDE(y(x,t))
>
> I would like to how to make the change of variable x = exp(z) where z
> is real. Is this possible?
>
> Thanks in advance
> Blair
> >
>
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