Re: control package, odd behavior multiplying tf's

[Sunil Shah]

Nothing in floating point arithmetic is really associative; only within numerical conditioning bounds.

Perhaps you are creating a Jordan structure, connecting identical  tf chains in series, and blowing up the matrix conditioning.   

Check the conditioning of the eigenvectors system matrix of the series connected system to see if this is the case.  

If each of the series connected system is numerically different, this problem goes away.  

Sunil Shah

On Fri, Jun 12, 2015 at 9:11 PM, Nicholas Jankowski <address@hidden> wrote:

>
> I confirm your results.
>
> I also tried a SISO system
>
>  a3=tf( [2 24],[1 4 7] )
>  a4=a3*a3
>  a5=a3*a4
>  a6=a4*a3
> but this worked correctly.
>
> a simpler example of your equation is:
>  a1 = tf({[2 24],[12];[1 48 0],[2 24]},{[-1 24],[-1 24];[-4 96],[-1 24]});
> a2=a1*a1;
> a3=a2*a1
> a4=a1*a2
>
>  
>
> --
> DAS
>

Thanks Doug. So, bug? Or some expected behavior I do not fathom yet?

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