D[Subscript[a, k],Subscript[a,j]] to return something like the Kronecker delta. Is this possible?
Of course, if you don't instist on logical correctness.
Subscript /: D[Subscript[a_, b_], Subscript[a_, c_]] := KroneckerDelta[b, c] Subscript /: D[ Subscript[a_, _], Subscript[b_, _]] := 0 /; a != b D[ Subscript[a,k], Subscript[a,j]] Subscript[\[Delta], j,k] D[ Subscript[a,k], Subscript[1,k]] 0
1$\begingroup$ I am not sure why
Subscript[\[Delta], j,k]appears in the code $\endgroup$ May 19 at 20:37
$\begingroup$ Probably you are able to Trace the answer easily. Evaluation algorithm produces terms Derivatives[1,0][Subscript] and Derivative[0,1][Subscript] . The rest is printers professional secret. $\endgroup$– Roland FMay 20 at 4:56
$\begingroup$ I think I might have understood what you did to get the
Subscript[\[Delta], j,k]. Maybe you used copy as then selected plain text rather than directly copy which would show
KroneckerDelta[j, k]. $\endgroup$ May 20 at 7:03