Re: NDSolve and vector functions

• To: mathgroup at smc.vnet.net
• Subject: [mg87953] Re: NDSolve and vector functions
• From: dh <dh at metrohm.ch>
• Date: Mon, 21 Apr 2008 03:25:17 -0400 (EDT)
• References: <fu9vl0\$ie2\$1@smc.vnet.net>

```
HI,

thank's a lot for the replies. I think the most practicable way is the

solution due to Carl. He packs all vector valued constants into

functions that only evaluate if the argument is numeric. I will play

around with this to check if there are no surprises.

thank's again, Daniel

dh wrote:

> Hello all,

>

> does anybody know a way to compute a vector valued function using

>

> NDSolve without explicitely specifying all vector components. Here is a

>

> simple example: Although NDSolve[{p'[t]==p[t],p[0]=={1,0}},p,{t,0,1}] works,

>

> NDSolve[{p'[t]==p[t]+{1,1},p[0]=={1,0}},p,{t,0,1}]

>

> does not work because p[t] in "p[t]+{1,1}"  is treated as a scalar and

>

> the expression is evaluated to {1+p[t],1+p[t]} what is clearly not

>

> intended. Even in "IdentityMatrix[2].p[t]+{1,1}"

>

> "IdentityMatrix[2].p[t]" is treated like a scalar and added to the

>

> components of {1,1}.

>

> do I miss something???

>

> Daniel

>

>

>

```

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