Re: NDSolve and derivative error
- To: mathgroup at smc.vnet.net
- Subject: [mg41401] Re: NDSolve and derivative error
- From: Racer X <rajduc at yahoo.com>
- Date: Sun, 18 May 2003 05:02:01 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
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