# Avoid error with DSolve (functions appear with no arguments)?

Posted 5 months ago
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 Hello =)I dont understand the DSolve Error i got on this differntial equations system. Some ideas? Thanks!
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Posted 5 months ago
 post your code using the code sample icon (the first one)
Posted 5 months ago
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 In[584]:= Subscript[B, v] = D[L, x'[t], t] - D[L, x[t]] Out[584]= 1. Subscript[\[Rho], Wasser] \[CurlyPhi][t] Derivative[1][x][t] Derivative[ 1][\[CurlyPhi]][t] + 1. M (x^\[Prime]\[Prime])[ t] - (-0.3 - 0.3 Subscript[\[Alpha], FlosseHinten] + 0.3 Subscript[\[Alpha], FlosseVorne]) Subscript[\[Rho], Wasser] (x^\[Prime]\[Prime])[t] + 0.5 Subscript[\[Rho], Wasser] \[CurlyPhi][t]^2 (x^\[Prime]\[Prime])[t] + 2 bv Derivative[1][x][t] (x^\[Prime]\[Prime])[t] + ( 4 M \[Pi] Subscript[l, Masse] (\[Phi]^\[Prime]\[Prime])[t])/ Derivative[1][\[Phi]][t]^2 In[585]:= Subscript[B, quer] = D[L, y'[t], t] - D[L, y[t]] Out[585]= 1. M (y^\[Prime]\[Prime])[t] + 2 Subscript[b, quer] Derivative[1][y][t] (y^\[Prime]\[Prime])[t] In[586]:= Subscript[B, beta] = D[L, \[Beta]'[t], t] - D[L, \[Beta][t]] Out[586]= -Subscript[b, beta] \[Beta][t]^2 - 0.000565056 E^(-0.28 Sqrt[\[Beta][t]^2]) M \[Beta][t]^5 + ( 0.0000263693 E^(-0.28 Sqrt[\[Beta][t]^2]) M \[Beta][t]^7)/Sqrt[\[Beta][t]^2] + 1. Subscript[J, \[Beta]] (\[Beta]^\[Prime]\[Prime])[t] In[587]:= Subscript[B, phi ] = D[L, \[CurlyPhi]'[t], t] - D[L, \[CurlyPhi][t]] Out[587]= -Subscript[b, phi] \[CurlyPhi][t]^2 + 0.0753408 E^(-0.23 Sqrt[\[CurlyPhi][t]^2]) M \[CurlyPhi][t]^3 - ( 0.0043321 E^(-0.23 Sqrt[\[CurlyPhi][t]^2]) M \[CurlyPhi][t]^5)/Sqrt[\[CurlyPhi][t]^2] - 0.5 Subscript[\[Rho], Wasser] \[CurlyPhi][t] Derivative[1][x][t]^2 + 1. Subscript[J, \[CurlyPhi]] (\[CurlyPhi]^\[Prime]\[Prime])[t] In[588]:= Subscript[B, omega ] = D[L, \[Phi]'[t], t] - D[L, \[Phi][t]] Out[588]= -Subscript[b, omega] \[Phi][t]^2 + ( 4 M \[Pi] Subscript[l, Masse] (x^\[Prime]\[Prime])[t])/ Derivative[1][\[Phi]][t]^2 + 1. Subscript[J, \[Phi]] (\[Phi]^\[Prime]\[Prime])[t] - ( 8 M \[Pi] Subscript[l, Masse] Derivative[1][x][t] (\[Phi]^\[Prime]\[Prime])[t])/ Derivative[1][\[Phi]][t]^3 In[589]:= In[590]:= In[595]:= DSolve[{Subscript[B, v] == 0, Subscript[B, quer] == 0, Subscript[B, phi ] == 0, Subscript[B, beta] == 0, Subscript[B, omega ] == 0, x[0] == 0 , x'[0] == Subscript[c, vv], y[0] == 0 , y'[0] == Subscript[c, vquer], \[Beta][0] == Subscript[c, sbeta], \[Beta]'[0] == Subscript[c, vbeta ], \[CurlyPhi][0] == Subscript[c, sphi] , \[CurlyPhi]'[0] == Subscript[c, vphi], \[Phi][0] == Subscript[c, somega], \[Phi]'[0] == Subscript[c, vomega]} , {x[t], y[t], \[CurlyPhi][t], \[Beta][t], \[Phi][t]} , t] During evaluation of In[595]:= DSolve::dvnoarg: The function \[CurlyPhi] appears with no arguments. Out[595]= DSolve[{1. Subscript[\[Rho], Wasser] \[CurlyPhi][t] Derivative[1][x][t] Derivative[ 1][\[CurlyPhi]][t] + 1. M (x^\[Prime]\[Prime])[ t] - (-0.3 - 0.3 Subscript[\[Alpha], FlosseHinten] + 0.3 Subscript[\[Alpha], FlosseVorne]) Subscript[\[Rho], Wasser] (x^\[Prime]\[Prime])[t] + 0.5 Subscript[\[Rho], Wasser] \[CurlyPhi][t]^2 (x^\[Prime]\[Prime])[t] + 2 bv Derivative[1][x][t] (x^\[Prime]\[Prime])[t] + ( 4 M \[Pi] Subscript[l, Masse] (\[Phi]^\[Prime]\[Prime])[t])/ Derivative[1][\[Phi]][t]^2 == 0, 1. M (y^\[Prime]\[Prime])[t] + 2 Subscript[b, quer] Derivative[1][y][t] (y^\[Prime]\[Prime])[t] == 0, -Subscript[b, phi] \[CurlyPhi][t]^2 + 0.0753408 E^(-0.23 Sqrt[\[CurlyPhi][t]^2]) M \[CurlyPhi][t]^3 - ( 0.0043321 E^(-0.23 Sqrt[\[CurlyPhi][t]^2]) M \[CurlyPhi][t]^5)/ Sqrt[\[CurlyPhi][t]^2] - 0.5 Subscript[\[Rho], Wasser] \[CurlyPhi][t] Derivative[1][x][t]^2 + 1. Subscript[J, \[CurlyPhi]] (\[CurlyPhi]^\[Prime]\[Prime])[t] == 0, -Subscript[b, beta] \[Beta][t]^2 - 0.000565056 E^(-0.28 Sqrt[\[Beta][t]^2]) M \[Beta][t]^5 + ( 0.0000263693 E^(-0.28 Sqrt[\[Beta][t]^2]) M \[Beta][t]^7)/ Sqrt[\[Beta][t]^2] + 1. Subscript[J, \[Beta]] (\[Beta]^\[Prime]\[Prime])[t] == 0, -Subscript[b, omega] \[Phi][t]^2 + ( 4 M \[Pi] Subscript[l, Masse] (x^\[Prime]\[Prime])[t])/ Derivative[1][\[Phi]][t]^2 + 1. Subscript[J, \[Phi]] (\[Phi]^\[Prime]\[Prime])[t] - ( 8 M \[Pi] Subscript[l, Masse] Derivative[1][x][t] (\[Phi]^\[Prime]\[Prime])[t])/ Derivative[1][\[Phi]][t]^3 == 0, x[0] == 0, Derivative[1][x][0] == Subscript[c, vv], y[0] == 0, Derivative[1][y][0] == Subscript[c, vquer], \[Beta][0] == Subscript[ c, sbeta], Derivative[1][\[Beta]][0] == Subscript[c, vbeta], \[CurlyPhi][0] == Subscript[c, sphi], Derivative[1][\[CurlyPhi]][0] == Subscript[c, vphi], \[Phi][0] == Subscript[c, somega], Derivative[1][\[Phi]][0] == Subscript[c, vomega]}, {x[t], y[t], \[CurlyPhi][t], \[Beta][t], \[Phi][t]}, t] 
 Beware that (x^\[Prime]\[Prime])[t] is not the same as x''[t], even though when typeset they look exactly alike. To enter the derivative sign use the apostrophe, as in the good old ascii days. You also use \[CurlyPhi] as a subscript, which may be the cause of the error message.