On Tuesday, 19 July 2016 20:49:19 UTC+2, Aaron Meurer wrote: > > IMHO, has() specifically should operate symbolically (no knowledge of > mathematics). > > Well, it's not really about knowledge of mathematics. It's about matching the unapplied element or the element applied with another argument.
> This old pull request seems relevant here > https://github.com/sympy/sympy/pull/7437. I think having methods for > objects to tell how to differentiate themselves is better than hacking > around the implementation details of the current implementation. > > I think f(x).diff(f(y)) should return 0, for the same reason that > x.diff(y) should return 0. We've had some in-depth discussions on what > differentiating with respect to a function should mean in SymPy, and the > thing we agreed on is that expr.diff(f(x)) should be the same as > expr.xreplace({f(x): y}).diff(y).xreplace({y: f(x)}). Specifically, > xreplace means it only looks at things structurally. > > OK, what about extending *Indexed* to support continuous indexing? *Indexed* is meant to represent a set of symbols, I think we could add a *continuous=True/False *option defaulting to *False* and have something like this: >>> A = Indexed("A") >>> A[i].diff(A[j]) KroneckerDelta(i, j) >>> B = Indexed("B", continuous=True) >>> var("x, y", real=True) >>> B[x].diff(B[y]) DiracDelta(x - y) The *KroneckerDelta *is already in the development branch. Kalevi, I think that generalizing the Dirac delta to complex numbers is a bit out of scope. Besides, do SymPy users really need it? -- You received this message because you are subscribed to the Google Groups "sympy" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. To post to this group, send email to [email protected]. Visit this group at https://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/2b2f5dac-01d8-44f3-942c-dfb301757dcd%40googlegroups.com. For more options, visit https://groups.google.com/d/optout.
