Hi, I'm not sure how to do the substitution, but why do you expect obj_function.diff(x) to be Derivative(Theta(U(x), x), x) + Derivative(U(x), x)* Derivative(Theta(U(x), x), U(x)) ?
I think the answer you are getting from sympy is not correct. obj_function.diff(x) should be the same as Derivative(Theta(U(x), x), x), but that is not what sympy is giving. See, https://github.com/sympy/sympy/issues/8510 CSymPy is giving, Derivative(U(x), x)*Subs(Derivative(Theta(_x, x), _x), (_x), (U(x))) + Subs(Derivative(Theta(U(x), _x), _x), (_x), (x)) which I think should be the correct answer. Here what Subs(Derivative(Theta(U(x), _x), _x), (_x), (x)) means is partial differentiate Theta with respect to the second variable and replace the first variable with U(x) and the second with x. (D[2](Theta)(U(x), x) is the equivalent in Maple syntax or Derivative[0, 1][Theta][U[x], x] in Mathematica syntax) Isuru Fernando On Fri, May 1, 2015 at 8:16 PM, Miguel Angel Salazar de Troya < salazardetr...@gmail.com> wrote: > Hello > > I have this derivative of a function that has an argument which is also a > function > > # Declaration > x = symbols('x') > U, Theta = symbols('U Theta', cls=Function) > > # Function to derive > obj_function = Theta(U(x),x) > > # Derivative > gradient_obj_function = obj_function.diff(x) > > And this is the output I obtain > > Derivative(Theta(U(x), x), x) + Derivative(U(x), > x)*Subs(Derivative(Theta(_xi_1, x), _xi_1), (_xi_1,), (U(x),)) > > How can I replace Subs(Derivative(Theta(_xi_1, x), _xi_1), (_xi_1,), > (U(x),)) with Derivative(Theta(U(x), x), U(x)) ? > I found this post, > https://groups.google.com/forum/#!searchin/sympy/"chain$20rule"/sympy/OfF5PklJtmY/t1FPWt3n8xIJ, > but it was not clear to me how this has to be done. > > Thanks > Miguel > > -- > 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 sympy+unsubscr...@googlegroups.com. > To post to this group, send email to sympy@googlegroups.com. > Visit this group at http://groups.google.com/group/sympy. > To view this discussion on the web visit > https://groups.google.com/d/msgid/sympy/5d9dfd23-be1a-4a08-9289-43562d0062f5%40googlegroups.com > <https://groups.google.com/d/msgid/sympy/5d9dfd23-be1a-4a08-9289-43562d0062f5%40googlegroups.com?utm_medium=email&utm_source=footer> > . > For more options, visit https://groups.google.com/d/optout. > -- 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 sympy+unsubscr...@googlegroups.com. To post to this group, send email to sympy@googlegroups.com. Visit this group at http://groups.google.com/group/sympy. To view this discussion on the web visit https://groups.google.com/d/msgid/sympy/CA%2B01voNocna%3D5Frerhb5Fy8nU59zdSPXnaO6A5SEXwp2cRZTeg%40mail.gmail.com. For more options, visit https://groups.google.com/d/optout.
