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 at http://groups.google.com/group/sympy?hl=en.
