Re: Is this solvable using Mathematica?

• To: mathgroup at smc.vnet.net
• Subject: [mg99089] Re: [mg99048] Is this solvable using Mathematica?
• From: "David Park" <djmpark at comcast.net>
• Date: Sun, 26 Apr 2009 01:41:14 -0400 (EDT)
• References: <19558021.1240650866679.JavaMail.root@n11>

```Don't you need a value for d?

David Park
djmpark at comcast.net
http://home.comcast.net/~djmpark/

From: johnboy98105 at yahoo.com [mailto:johnboy98105 at yahoo.com]

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.