On Sep 11, 2010, at 5:04 AM, Bastian Weber wrote: > Aaron S. Meurer wrote: >> Well, Chris is right that the problem directly is issue 2049, but >> actually, the reason that you get the problem is that what you are >> trying to do is not yet supported, namely, taking derivatives with >> respect to functions. See issue 1816. >> >> So a workaround will have to be to temporarily replace x(t) with just >> the symbol x (or some other dummy symbol), until that becomes >> implemented. > > > OK, thanks so far. > However, I think just replacing x(t) by a symbol does serve for me since > I want to take the total derivative with respect to t. > > Additionally, it seems to me that taking derivatives with respect > functions is supported at least partially. > E.g. > > In [3]: f(x(t)).diff(t) > Out[3]: D(f(x(t)), x(t))*D(x(t), t)
That is a bug. Really, there is no way to support f(x(t)).diff(t) without support for f(x(t)).diff(x(t)). So the chain rule code creates that Derivative, but the other derivative code doesn't know how to handle it correctly, and so it ends up creating problems. > > works as expected. > > > Meanwhile I found a workaround for my problem: > Replacing D(f(x(t)), x(t)) by a symbol (say z), perform the substitution > that I actually want to do, i.e., replacing D(x(t), t) by the Symbol a > and finally resubstitute z by D(f(x(t)), x(t)) > > Of course it would be much better if this would work directly. > > BTW is there a notifying mechanism if an issue gets solved? Click on the star icon on the issue page. > > Thanks again. Bastian. Aaron Meurer -- 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.
