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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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