Re: NDSolve and derivative error
- To: mathgroup at smc.vnet.net
- Subject: [mg41421] Re: NDSolve and derivative error
- From: "Kevin J. McCann" <KevinMcCann!kjm at uunet.uu.net>
- Date: Mon, 19 May 2003 05:09:40 -0400 (EDT)
- References: <ba7ho3$5en$1@smc.vnet.net>
- Sender: owner-wri-mathgroup at wolfram.com
This works for me. r=2.5*10^-6; nsol = NDSolve[{0.005*x[t]*Derivative[1][x][t] == 0.148 + 0.00005*UnitStep[t] - (0.006*x[t]*Derivative[1][x][t])/r, x[0] == 10^(-6)}, x[t], {t, 0, 0.05}, AccuracyGoal -> 20, WorkingPrecision -> 25, MaxSteps -> Infinity][[1]] Plot[x[t]/.nsol,{t,0,0.05}]; "Racer X" <rajduc at yahoo.com> wrote in message news:ba7ho3$5en$1 at smc.vnet.net... > > Hi Kevin, > > Sorry Kevin, thought I'd substituted all the > constants. r is equal to 2.5e-6. > > Raj > > --- "Kevin J. McCann" <kjm at KevinMcCann.icomcast.net> > wrote: > > On the RHS you have 0.006/r. What is r? > > > > > > "Racer X" <rajduc at yahoo.com> wrote in message > > news:ba50fq$s9s$1 at smc.vnet.net... > > > > > > Hi, > > > > > > I have been using Mathematica on and off for about > 10 > > > years, but am not really an expert. I have been > > > unable to get beyond this problem: > > > > > > NDSolve[{0.005*x[t]*Derivative[1][x][t] == 0.148 + > > > 0.00005*UnitStep[t] - > > > (0.006/r)*x[t]*Derivative[1][x][t], x[0] == > 1.*^-6}, > > > x, {t, 0, 0.05}, AccuracyGoal -> 20, > WorkingPrecision > > > -> 25, MaxSteps -> Infinity] > > > > > > I get the following error: > > > > > > NDSolve::"ndnum" : "Encountered non-numerical > value > > > for a derivative at t == \0." > > > > > > This problem relates to the speed which water will > > > rise in a capillary tube. It has an analytical > > > solution, but I want to be able to vary the > UnitStep > > > input to an arbitrary pulse and need the above to > > > work. > > > > > > Any suggestions? Thanks! > > > > > > Raj > > > > __________________________________ > Do you Yahoo!? > The New Yahoo! Search - Faster. Easier. Bingo. > http://search.yahoo.com >