Na, Udo hat das doch alles schön gelöst.

Perhaps everything gets clearer when you substitue the K[ i ] by other variables:

DSolve[a x[t] + g x'[t] + x''[t] == F[t], x[t], t] /.   K[1] -> \[Xi] /. K[2] -> \[Eta]

But then remains the question what do you mean by xi[ t ]? They seem to be discrete values, which are to be represented by a function F[ t ].

I understand it like this: to each t ( the specific t valid for xi ) you go to calculate

A[t] = Sum[ x[i, t], {i, 2, n}]

and you will get a set of A - values (for the given t's) representing the value of F for that t. And now you construct an Interpolation - Function (see Interpolation in the help-menu) which you could pass to the solution of your DGL.

But I am afraid the Integration in this case will only work numerically.

Regards Hans

Thank you for your reply. In the second Output, i do not understand waht the K[1], K[2] stands for. Furthermore I do not know what F[K[1]] stands for. What should i interpret? I have F[t]=$\sum{i=2}^\infty bi x_i[t]$ . What is F[K[1]]?

I have a discrete t. The xi[t] are time series like x1=[3,6,8,9,...,n], x_2=[6,9,10,12,...,n] etc. for an example.

Regards Julia

Hallo Hans,

danke für die schnelle Antwort.

Ich würde dort also die Summe erneut einsetzen und anstatt [t] dann [K[1]], oder? Meinst du das damit? Das heißt, um das explizit lösen zu können, muss ich dann ebenfalls das Integral berechnen, nicht wahr?

Puh, ich habe mir das irgendwie schöner vogestellt. :D

VG Julia