       Re: Re: NDSolve problem

• To: mathgroup at smc.vnet.net
• Subject: [mg101701] Re: [mg101676] Re: NDSolve problem
• From: Haibo Min <yshdfeng at gmail.com>
• Date: Wed, 15 Jul 2009 07:06:07 -0400 (EDT)
• References: <h3cfav\$ic8\$1@smc.vnet.net> <200907140934.FAA01779@smc.vnet.net>

```Thank you very much, Simon.
After adding the definition, it seems that methematica does recognize the
e1,e2 and CurlyTheta and no error indications such as
"Part::partw: Part 2 of e1[t] does not exist" occur.
EE is in fact a 4x3 matrix. I think my equation is right since I verified
all the RHS of the equation (after defining e1,e2 and CurlyTheta
respectively) and they are all right.

But now new problem occurs, in the NDSolve part, it tells me that:
NDSolve::ndode: Input is not an ordinary differential equation.

I feel very puzzled, since the equation is INDEED a differential equation
with e1,e2 and CurlyTheta  as its variables..I checked for many times, but
is?

Thank you again!
Best regards,
Haibo

On Tue, Jul 14, 2009 at 5:34 PM, Simon <simonjtyler at gmail.com> wrote:

> Hi Haibo
>
> Mathematica does not have built in support for abstract linear algebra
> quantities, so if something is a vector or a matrix then you have to
> give it components.
> Define (for example)
> e1[t_] := {e11[t], e12[t], e13[t], e14[t]}
> e2[t_] := {e21[t], e22[t], e23[t]}
> \[CurlyTheta][t_] := {\[CurlyTheta]1[t], \[CurlyTheta]2[t], \
> [CurlyTheta]3[t]}
>
> Then, the second problem with your code is that the matrices S, G and
> J are 3x3, whilst EE is a 4x4 -- you seem to be mixing these in your
> differential equations.
> For example, the first line in your NDSolve is
> J.e2'[t] == -kq Transpose[EE[e1[t]]].e1[t]-...
> on the RHS you have a 4-vector minus a whole heap of 3-vectors, on the
> LHS a 3-vector.
>
> Fix these two problems and it should all work....
>
> Simon
>
>

```

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