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Re: Is this solvable using Mathematica?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg99117] Re: Is this solvable using Mathematica?
  • From: dh <dh at metrohm.com>
  • Date: Mon, 27 Apr 2009 05:25:13 -0400 (EDT)
  • References: <gsuiqn$dq8$1@smc.vnet.net>


Hi,

this system of equations is under determined. You have a second order 

DEQ in a, what needs 2 equation and 1 first order DEQ in b, what needs 

another equation. Therefore, you will need 3 equations.

Daniel





johnboy98105 at yahoo.com wrote:

> Supposed you want to define a second order derivative along with your

> ODEs. (So you can scale the second order term)

> 

> Example shown below.

> 

> k1 = 1;

> r1 = 1;

> NDSolve[{a'[t] == k1 b[t] - d, a''[t] == r1 b'[t], a'[0] == 0, a[0] ==

> 1, b[0] == 0}, {a[t], b[t]}, {t, 1, 10} ]

> 

> But I get an error.

> 

> NDSolve::ntdvmm:

> Cannot solve to find an explicit formula for the derivatives.  NDSolve

> will try solving the system using a mass matrix method.

> 

> NDSolve::ndnum: Encountered non-numerical value for a derivative at t

> == 0.`.

> 

> Maybe this is more of a math question than software. But I would be

> very interested in seeing if it's doable in Mathematica.

> 

> Thanks in advance.

> 

> 




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