How do i put last equation, eqm[x, t, k, n] into matrix form? I want every row to end with == 0


n = 3; 
Subscript[k, (j_)?EvenQ] = κ; 
Subscript[k, (j_)?OddQ] = k; 
Subscript[k, (j_)?0] = ko; 
Subscript[k, (j_)?n + 1] = ko; 

ue[x_, t_, k_, n_] := 
  (1/2) *
      Subscript[k, j]*(Subscript[x, j - 1][t] - Subscript[x, j][t])^2,
      {j, 1, n + 1}]; 

te[x_, t_, n_] := 
  (1/2)*m*Sum[Derivative[1][Subscript[x, j]][t]^2, {j, 1, n}]; 

lg[x_, t_, k_, n_] := te[x, t, n] - ue[x, t, k, n]; 

eqm[x_, t_, k_, n_] := 
   Sum[D[lg[x, t, k, n], {Subscript[x, j][t], 1}], {j, 1, n}] - 
   Sum[D[D[lg[x, t, k, n], {Derivative[1][Subscript[x, j]][t], 1}], 
     {t, 1}], {j, 1, n}];

MatrixForm[eqm[x, t, k, n]] == MatrixForm[0]

I want it to look like this but with zero on the other side

enter image description here

For n = 3 It should look like this:

enter image description here

I tried array, but I'm bad at such stuff! I was able to do it correctly some time ago. It was short. Unfortunately, I deleted some files, so I lost the correct code.

  • $\begingroup$ why you vote down !? This is regular question! $\endgroup$
    – nufaie
    Apr 2, 2019 at 14:27
  • 1
    $\begingroup$ The output of eqm[x, t, k, n] is a single equation. What do you mean by "putting it in matrix form"? Also, avoid subscripts if you can; they tend to complicate expressions needlessly. You will also notice that MatrixForm[0] doesn't really make much sense. Show us an example of the output you seek. $\endgroup$
    – MarcoB
    Apr 2, 2019 at 14:29
  • $\begingroup$ check now i edit added a pic $\endgroup$
    – nufaie
    Apr 2, 2019 at 14:36
  • $\begingroup$ duplicate of mathematica.stackexchange.com/q/194153 ? $\endgroup$
    – Roman
    Apr 2, 2019 at 14:37
  • $\begingroup$ every j in the sum in eqm generate a dimension and row for the matrix. how using array and tables can i sort them put them finally in matrix form. i did it sometime ago but deleted some old files so i got lost ! $\endgroup$
    – nufaie
    Apr 2, 2019 at 14:38

1 Answer 1


this one way to do it !

q1 = Table[eq[x, t, k, n][[j]], {j, 1, n}] // Simplify
q2 = Table[eq[x, t, k, n][[j]], {j, n + 1, 2 n}]

MatrixForm[q1 + q2] == MatrixForm[Table[0, {j, 1, n}]]

enter image description here


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