First I would like to get the output of

F[x_, y_, k_] := Sum[x^(m - n)*y^m, {n, 0, k}, {m, n, k - 1}]

as an unevaluated (symbolic) sum. Then, derivate F

D[F[x, y, k], x]

and also get the derivative as an unevaluated sum. ¿Is it possible?


You can use Inactive:

F[x_, y_, k_] := Inactive[Sum][x^(m - n)*y^m, {n, 0, k}, {m, n, k - 1}]


D[F[x,y,k], x]

Inactive[Sum][(m x^(-1 + m - n) - n x^(-1 + m - n)) y^m, {n, 0, k}, {m, n, -1 + k}]

In Mathematica, the above is rendered as:

enter image description here


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.