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" <[email protected]> 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 [email protected]. > > To unsubscribe from this group, send email to > > [email protected]. > > 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 [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/sympy?hl=en.
