# Sum and Derivate

Posted 9 years ago
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 I want to programm a N-Pendulum(the Idea comes from the Doublependulum). And i have the following Problem:v[q_]:=Sum[Subscript[l, n]Sin[Subscript[\[Phi], n][t]],{n,1,q,1}]w[q_]:=Sum[-Subscript[l, n]Cos[Subscript[\[Phi], n][t]],{n,1,q,1}]vko=Subscript[l, 1]Sin[Subscript[\[Phi], 1][t]]wko=-Subscript[l, 1]Cos[Subscript[\[Phi], 1][t]]These are the Koordinates of for the mass of the first pendulum. But what happens now is more a technical problem of mathematica, i think. I put the first point (v,w) in to the kinetic energy:Tkin = Sum[  Subscript[m, q]/2 (D[v[q], t]^2 + D[w[q], t]^2), {q, 1, 1, 1}]Out: 1/2 Subscript[m, 1] (Cos[Subscript[\[Phi], 1][t]]^2   \!$$\*SubsuperscriptBox[\(l$$, $$1$$, $$2$$]\) Derivative[1][       Subscript[\[Phi], 1]][t]^2 + Sin[Subscript[\[Phi], 1][t]]^2   \!$$\*SubsuperscriptBox[\(l$$, $$1$$, $$2$$]\) TextCell[      ""]^2 Derivative[1][Subscript[\[Phi], 1]][t]^2)The Second Point (vko,wko)Tkin = Sum[  Subscript[m, q]/2 (D[vko, t]^2 + D[wko, t]^2), {q, 1, 1, 1}]Out: 1/2 Subscript[m, 1] (Cos[Subscript[\[Phi], 1][t]]^2   \!$$\*SubsuperscriptBox[\(l$$, $$1$$, $$2$$]\) Derivative[1][       Subscript[\[Phi], 1]][t]^2 + Sin[Subscript[\[Phi], 1][t]]^2   \!$$\*SubsuperscriptBox[\(l$$, $$1$$, $$2$$]\) Derivative[1][       Subscript[\[Phi], 1]][t]^2)In the first Out u see: mathematica put  " ^2" in the solution. But when i give mathematica the koord without the sum, it gives the correct solution without the Textcell[""]^2.How can i bring mathematica to stop generating this Textcell?