NDSolve and derivative error
- To: mathgroup at smc.vnet.net
- Subject: [mg41379] NDSolve and derivative error
- From: Racer X <rajduc at yahoo.com>
- Date: Sat, 17 May 2003 05:47:50 -0400 (EDT)
- Sender: owner-wri-mathgroup at wolfram.com
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
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