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
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