You're talking about Symbol._eval_derivative? I tried that within my
extended Symbol class. It returns 0 or 1 testing self == symbol. I
tried making some changes to it, but I don't think I can use it. I
think it doesn't even get called unless you do something like:
t = timevaryingsymbols('t')
Derivative(2+3*t,t)
I think only when t is both part of (expr, symbols, ...) within
Derivative's __new__ definition does t's _eval_derivative() method get
called.
-Gilbert
On Jun 3, 6:53 pm, Aaron Meurer <asmeu...@gmail.com> wrote:
> Can you just get what you want by overriding _eval_derivative()?
>
> Aaron Meurer
>
>
>
>
>
>
>
> On Fri, Jun 3, 2011 at 7:48 PM, Gilbert gede <gilbertg...@gmail.com> wrote:
> > I guess I should have asked this as well; is it considered bad to
> > write diff() and replace the current Sympy diff() within my code? Or
> > is that OK?
>
> > -Gilbert
>
> > On Jun 3, 6:38 pm, Gilbert gede <gilbertg...@gmail.com> wrote:
> >> Yeah, I had read some of them. I had already thought of writing my
> >> own Diff method or something and do substitution with it, but was
> >> hoping to have the functionality I want work like standard SymPy
> >> operations. That's what I've been trying to do with my PyDy classes;
> >> make them work more like you would expect other SymPy objects to.
> >> I have read through Derivative() and diff(), and couldn't really find
> >> a way to make them do what I want (like I said about my symbol
> >> extension no longer having its methods called once it is inside a
> >> SymPy add or mul). I guess what I was hoping for was input on whether
> >> I could make Derivative do what I want with my extended Symbol, as I
> >> couldn't really see how. But if writing my own Diff method is the
> >> only option, there's not much I can do then.
>
> >> Thanks,
> >> -Gilbert
>
> >> On Jun 3, 5:53 pm, "Aaron S. Meurer" <asmeu...@gmail.com> wrote:
>
> >> > This has actually been discussed quite a bit before (a lot of people
> >> > want to use Lagrangians). You can search the mailing list. From what
> >> > I've seen, you will either have to write your own custom diff routine or
> >> > do clever substitution of functions and derivatives with symbols. I
> >> > don't think I've ever seen anyone suggest extending Symbol to hold a
> >> > time derivative, which is essentially just a more formal way of doing
> >> > the substation method. It might work.
>
> >> > Aaron Meurer
>
> >> > On Jun 3, 2011, at 6:05 PM, Gilbert Gede wrote:
>
> >> > > Hi,
> >> > > I was trying to implement some functionality for PyDy for this year's
> >> > > GSoC, and was looking for some advice.
> >> > > In dynamics problems, you usually have time-varying quantities, like
> >> > > generalized coordinates, speeds, and accelerations. Often, you want
> >> > > to take the partial derivative of an expression with respect to the
> >> > > time derivative of one of these quantities. This come up when using
> >> > > Lagrange's Method (or Kane's Method). It's described to some degree
> >> > > here:
> >> > >http://en.wikipedia.org/wiki/Lagrangian_mechanics
> >> > >https://gist.github.com/1005937
> >> > > In Lagrange's Method, you end up taking the partial derivative of the
> >> > > energy with respect to the time derivative of a generalized
> >> > > coordinate. I'm trying to figure out a way to make this work in
> >> > > PyDy/SymPy. Derivative won't take in anything but a Symbol.
> >> > > The only idea I have come up with is to extend Symbol and write my own
> >> > > .diff() method for it which returns a new symbol representing the time
> >> > > differentiation of the original extended Symbol. Once my new object
> >> > > is inside a Mul or Add sympy object, then my .diff() method is no
> >> > > longer called.
> >> > > Can anyone give some insight into how I could get this desired
> >> > > behavior, taking the derivative of an expression wrt a
> >> > > time-differentiated symbol, to work in a way consistent with existing
> >> > > SymPy behavior? Thanks.
>
> >> > > -Gilbert
>
> >> > > --
> >> > > You received this message because you are subscribed to the Google
> >> > > Groups "sympy" group.
> >> > > To post to this group, send email to sympy@googlegroups.com.
> >> > > To unsubscribe from this group, send email to
> >> > > sympy+unsubscr...@googlegroups.com.
> >> > > For more options, visit this group
> >> > > athttp://groups.google.com/group/sympy?hl=en.
>
> > --
> > You received this message because you are subscribed to the Google Groups
> > "sympy" group.
> > To post to this group, send email to sympy@googlegroups.com.
> > To unsubscribe from this group, send email to
> > sympy+unsubscr...@googlegroups.com.
> > For more options, visit this group
> > athttp://groups.google.com/group/sympy?hl=en.
--
You received this message because you are subscribed to the Google Groups
"sympy" group.
To post to this group, send email to sympy@googlegroups.com.
To unsubscribe from this group, send email to
sympy+unsubscr...@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/sympy?hl=en.
