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Re: A simple ordinary differential equation



Hi,

look at: f[x_?NumericQ] = 1 - 1111*x'^2

you can not take the derivative of a number.

Daniel



I. Shechtman wrote:

> What is wrong with this equation?

> 

> Clear[sol]

> f[x_?NumericQ] = 1 - 1111*x'^2;

> sol = NDSolve[{x''[t] + (16/10^4)x'[t]^2*Sqr[

> f[x[t]]]/x[

>     t]^2 - (1458/10^9)*f[x[t]]/x[t]^2 == 

>             0, x[0] == 1, x'[0] == 0}, x[t], {

>               t, 0, 100}, AccuracyGoal -> 8,

>                      PrecisionGoal -> 8, WorkingPrecision -> 

>                   30, MaxSteps -> Infinity];

> Plot[Evaluate[x'[t] /. sol], {t, 0, 100}]

> 




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