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 Author Comment/Response Dr. Frank Solina Gilbert 09/28/05 6:01pm Hi @all :), First of all. I am a newbie in using mathematica. Please be patient. I have developed a mathematical model in form of an differential equation for my task. Now, I want to fit my data consisting of a set of 500 points (x1,x2,y). So I wrote the following code. \!\(HSE[A_?NumberQ, B_?NumberQ, C_?NumberQ, D_?NumberQ] := Block[{sol, f}, sol = \(NDSolve[{\((A + B\ Abs[f[t]] + C\ f[t]\^2 + D\ Abs[f[t]\^3])\)\ f[ t] + C\ \(f'\)[ t] == \ 0\ , f[0] == 0}, f, {t, 0, 500}, Method -> "\"]\)[\([1]\)]; Plus @@ \ Apply[\((f[#1] - #2)\)^2 &, data, { 1}] /. sol]; \ NMinimize[HSE[A, B, C, D], {A, B, C, D}, \ Method -> "\"]\) Solving this problem with a data set of 2 colums is not a problem, but I get an error message, if I use a data set with 3 colums like the following one: ata = {{1.0, 0.014, 0.01}, {2.0, 1.4, 1.5}, {1.005, 2.1104, 4.44}, {8.0, 3.0, 0.144}, {.1, -.1, 0.114}}; I want to use the thirth colum as my vibration initiator. Then the code above becomes like this: \!\(HSE[A_?NumberQ, B_?NumberQ, C_?NumberQ, D_?NumberQ] := Block[{sol, f}, sol = \(NDSolve[{\((A + B\ Abs[f[t]] + C\ f[t]\^2 + D\ Abs[f[t]\^3])\)\ f[ t] + C\ \(f'\)[t] == \ g[t]\ , f[ 0] == 0}, f, {t, 0, 500}, Method -> "\"]\)[\([1]\)]; Plus \ @@ Apply[\((f[#1] - #2)\)^2 &, data, {1}] /. sol]; \ NMinimize[HSE[A, B, C, D], {A, B, C, D}, \ Method -> "\"]\) Mathematica says that the number of equations do no not match the number of parameters. I don't know waht to say, I am using Mathematica only since one week. I would really appreatiate it, if someone could tell that I used a wrong syntax in my code. Thnaks in advance, for your help. Franc Solina Gilbert URL: ,

 Subject (listing for 'Data Fitting to Differential Equations') Author Date Posted Data Fitting to Differential Equations Dr. Frank So... 09/28/05 6:01pm Re: Data Fitting to Differential Equations yehuda ben-s... 09/30/05 00:25am Re: Data Fitting to Differential Equations Frank Solina... 09/30/05 4:12pm Re: Data Fitting to Differential Equations Frank Solina... 10/01/05 08:26am Re: Data Fitting to Differential Equations yehuda ben-s... 10/02/05 2:20pm Re: Data Fitting to Differential Equations FRanc Solina... 10/05/05 4:48pm Re: Data Fitting to Differential Equations Franc Solina... 10/13/05 09:12am
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