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 Author Comment/Response Rupert 12/02/07 12:42pm I am trying to solve a system of two coupled ODES using NDSolve: In[1]:= \!\(eqn1 = a[t]*b[ t]\^2 - \((\((a[t]/b[t]^2)\) - \(( 1/a[t])\))\) + \((t\^2)\)*b[t] == \(b''\)[t]\[IndentingNewLine] eqn2 = \(( a\^2)\)[t]*b[t] + \((\((1/b[t])\) - \((b[t]/\((a\^2)\)[ t])\))\) == \(a''\)[t]\) Out[1]= \!\(\* RowBox[{\(1\/a[t] - a[t]\/b[t]\^2 + t\^2\ b[t] + a[t]\ b[t]\^2\), "\[Equal]", RowBox[{ SuperscriptBox["b", "′′", MultilineFunction->None], "[", "t", "]"}]}]\) Out[2]= \!\(\* RowBox[{\(1\/b[t] - b[t]\/\(a\^2\)[t] + \(a\^2\)[t]\ b[t]\), "\[Equal]", RowBox[{ SuperscriptBox["a", "′′", MultilineFunction->None], "[", "t", "]"}]}]\) In[3]:= sol=NDSolve[{eqn1,eqn2, a[0]==b[0]\[Equal]0,a'[0]\[Equal]b'[0]==1},{a,b},{t,30}] From In[3]:= \!\(\* RowBox[{\(NDSolve::"dvnoarg"\), \(\(:\)\(\ \)\), "\<\"The function \\!\\( a\\) appears with no arguments. \\!\\(\\*ButtonBox[\\\"More…\\\", \ ButtonStyle->\\\"RefGuideLinkText\\\", ButtonFrame->None, \ ButtonData:>\\\"NDSolve::dvnoarg\\\"]\\)\"\>"}]\) Out[3]= \!\(\* RowBox[{"NDSolve", "[", RowBox[{ RowBox[{"{", RowBox[{ RowBox[{\(1\/a[t] - a[t]\/b[ t]\^2 + t\^2\ b[t] + a[t]\ b[t]\^2\), "\[Equal]", RowBox[{ SuperscriptBox["b", "′′", MultilineFunction->None], "[", "t", "]"}]}], ",", RowBox[{\(1\/b[t] - b[t]\/\(a\^2\)[t] + \(a\^2\)[t]\ b[t]\), "\[Equal]", RowBox[{ SuperscriptBox["a", "′′", MultilineFunction->None], "[", "t", "] "}]}], ",", \(a[0] \[Equal] b[0] \[Equal] 0\), ",", RowBox[{ RowBox[{ SuperscriptBox["a", "′", MultilineFunction->None], "[", "0", "]"}], "\[Equal]", RowBox[{ SuperscriptBox["b", "′", MultilineFunction->None], "[", "0", "]"}], "\[Equal]", "1"}]}], "}"}], ",", \({a, b}\), ",", \({t, 30}\)}], "]"}]\) but I keep getting the error message NDSolve::dvnoarg: The function a appears with no arguments. Can someone tell me what is wrong with my input? Attachment: Coupled Eqn 2.nb, URL: ,

 Subject (listing for 'NDSolve Coupled ODEs') Author Date Posted NDSolve Coupled ODEs Rupert 12/02/07 12:42pm Re: NDSolve Coupled ODEs Peter Diehr 12/20/07 12:26pm
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