Re: A simple ordinary differential equation
- To: mathgroup at smc.vnet.net
- Subject: [mg98211] Re: [mg98201] A simple ordinary differential equation
- From: "Pasha Karami" <karami at geo.uu.nl>
- Date: Fri, 3 Apr 2009 04:32:14 -0500 (EST)
- References: <200904020948.EAA22322@smc.vnet.net>
Hi, I think you are doing few mistakes: 1) you miss "t" in the Sqrt function 2) you define a function f as a function of x which does not include t. Better not to do that ans simply put this term in your equations; but check it first if I am right. 3)You solve equations for x[t] but you plot for x'[t]. Since it is numerically solve better to solve equations for x'[t]. I have the modified code below but not sure if it is really true. Please check it first. Clear[sol] sol = NDSolve[{x''[t] + (16/10^4) x'[t]^2* Sqrt[(1 - 1111*x'[t]^2)]/ x[t]^2 - (1458/10^9)*(1 - 1111*x'[t]^2)/x[t]^2 == 0, x[0] == 1, x'[0] == 0}, x'[t], {t, 0, 100}, AccuracyGoal -> 0, PrecisionGoal -> 0, MaxSteps -> Infinity]; Plot[Evaluate[x'[t] /. sol], {t, 0, 100}] Regards, Pasha > 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}] > > PhD student "Pasha Karami" Room z.206,Dept. of Earth Sciences Utrecht University Budapestlaan 4 3584 CD Utrecht The Netherlands Tel:+31-30-2537503
- References:
- A simple ordinary differential equation
- From: "I. Shechtman" <shechtma@netvision.net.il>
- A simple ordinary differential equation