       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>

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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, a ==

> 1, b == 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.

>