[ODE] world update - best practices?

Patrick Enoch Hendrix_ at gmx.net
Fri May 25 01:28:35 MST 2007

No, the solver will become unconditionally unstable. Sounds nasty -  
and it is indeed.

You can identify this behaviour by looking at a single error-element:
it will spike very positive and then very negative. If you sum up the  
absolute value of all elements, the error will be monotonic  
increasing all the time rapidly.

It is okay for the error-sum to go up for several iterations, this is  
part of the SOR algorithm. A very large error in one element will  
spread across the other connected elements (e.g. connected by a  
joint), to find a global solution later on.

The default value for omega ("W") is 1.3 in ODE. And it appears to  
work well for everybody. You should leave it this way.


On 25. May 2007, at 1:45 Uhr, Mark Williams wrote:

>> Note: you can set a "W" smaller than 1.0. This is not "foolish" as
>> stated in the linked articel - it is called "underrelaxation". But
>> you dont need that for constant matrices.
> Thanks. Would there ever be a valid reason to set it above 2.0?
> Mark
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