Re: NDSolve and derivative error
- To: mathgroup at smc.vnet.net
- Subject: [mg41420] Re: [mg41379] NDSolve and derivative error
- From: Bobby Treat <drmajorbob+MathGroup3528 at mailblocks.com>
- Date: Sun, 18 May 2003 05:05:14 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
r=2.5e-6. is ALSO not numeric. Try r = 2.5*10^-6. Bobby -----Original Message----- From: Racer X <rajduc at yahoo.com> To: mathgroup at smc.vnet.net Subject: [mg41420] Re: [mg41379] NDSolve and derivative error Dear Selwyn & Bob, Thanks for replying. 'r' is actually defined and I forgot to put in its numerical value into the quoted formula for NDSolve. Please try the equation with r=2.5e-6. Apologies for my forgetfulness. Regards, Raj --- Bobby Treat <drmajorbob at mailblocks.com> wrote: > r is not numerical, so NDSolve can't deal. > > Bobby > > -----Original Message----- > From: Racer X <rajduc at yahoo.com> To: mathgroup at smc.vnet.net > To: mathgroup at smc.vnet.net > Sent: Sat, 17 May 2003 05:47:50 -0400 (EDT) > Subject: [mg41420] [mg41379] NDSolve and derivative error > > > 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