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Re: NDSolve Unable to find initial conditions that satisfy the

  • To: mathgroup at smc.vnet.net
  • Subject: [mg116598] Re: NDSolve Unable to find initial conditions that satisfy the
  • From: Oliver Ruebenkoenig <ruebenko at wolfram.com>
  • Date: Mon, 21 Feb 2011 05:34:32 -0500 (EST)

On Sun, 20 Feb 2011, Ali K. Ozdagli wrote:

> Any help?
>
> On Fri, Feb 11, 2011 at 8:25 PM, Ali K. Ozdagli <ozdagli at gmail.com> wrote:
>
>> Hello all,
>>
>> When I write the following to mathematica
>>
>> NDSolve[{0.04*u[z, t] == -3*(D[u[z, t], z])^(1/3) + 0.02*z*D[u[z, t], z] -
>> D[u[z, t], t], Derivative[1, 0][u][1, t] == 0, u[z, 0] == 0}, u, {z, 1, 2},
>> {t, 0, 1}, MaxSteps -> 10^4, AccuracyGoal -> 8, SolveDelayed -> True];
>>
>> Although the solution is relatively easy, u[z,t]=0, it gives the following
>> errors:
>>
>> NDSolve::ibcinc: Warning: Boundary and initial conditions are inconsistent.
>>>>
>>
>> NDSolve::icfail: Unable to find initial conditions that satisfy the
>> residual function within specified tolerances. Try giving initial conditions
>> for both values and derivatives of the functions >>
>>
>>
>> I do not see any inconsistency in the boundary conditions and don't know
>> why mathematica cannot find a solution.
>>
>> Any help is appreciated.
>>
>> Best,
>>
>> Ali
>>
>>
>
>
>
Ali,

if you use

NDSolve[{0.04*u[z, t] == -3*(D[u[z, t], z])^(1/3) +
      0.02*z*D[u[z, t], z] -
      D[u[z, t], t], Derivative[1, 0][u][1, t] == 0, u[z, 0] == 0},
   u, {z, 1, 2},
   {t, 0, 1}, MaxSteps -> 10^4, AccuracyGoal -> 8];

you get the following message:

The differential order of the functions in the initial or boundary \
conditions should be strictly less than in the differential equations.

This means that for the present eqn the boundary condition must 
not contain a derivative.

Oliver


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