Re: NDSolve and derivative error
- To: mathgroup at smc.vnet.net
- Subject: [mg41403] Re: [mg41379] NDSolve and derivative error
- From: Selwyn Hollis <selwynh at earthlink.net>
- Date: Sun, 18 May 2003 05:02:20 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
Hi Raj, There's an r in your equation that you forgot to define. ----- Selwyn Hollis http://www.math.armstrong.edu/faculty/hollis On Saturday, May 17, 2003, at 05:47 AM, Racer X wrote: > > 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 > >