Re: [Boost-users] odeint feedback request

Subject: Re: [Boost-users] odeint feedback request
From: Karsten Ahnert (karsten.ahnert_at_[hidden])
Date: 2011-10-25 15:23:03

On 10/25/2011 01:20 PM, Larry Evans wrote:
> The page:
> 
> http://headmyshoulder.github.com/odeint-v2/doc/boost_sandbox_numeric_odeint/getting_started/short_example.html
> 
> says:
> 
>   The equations of motion are given by x'' = -x + γ x'. This can be
>   transformed to a system of two coupled first-order differential
>   equations with new variables x and p=x'. To apply numerical
>   integration one first has to design the right hand side of the
>   equation w' = f(w) where in this case w = (x,p):
> 
> which initially confused me because x was not a new variable as
> claimed by:
> 
>   new variables x and p=x'
> 
> I think it would be clearer if it read:
> 
>   with new variables w_1=x and w_2=x'.
> 
> and then:
> 
>   w = (w_1,w_2)
> 
> which would emphasize that w was a vector and f was a function taking
> a vector and returning a vector.

Ok, you are right. It is pedagogical not very clever. I will change it.
Btw. this method can always be applied to transform any higher-order ODE
into a system of coupled first order ODEs.

Best regards,

Karsten

> 
> -regards,
> Larry
> 
> 
> 
> 
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