       Re: Is this solvable using Mathematica?

• To: mathgroup at smc.vnet.net
• Subject: [mg99091] Re: Is this solvable using Mathematica?
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Sun, 26 Apr 2009 01:41:35 -0400 (EDT)
• References: <gsuiqn\$dq8\$1@smc.vnet.net>

```Hi,

this is not solvable at all, because one equation (for a''[t] or b[t])
is missed.

Regards
Jens

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.
>