[aspect-devel] Problem: Iterative advection solver does not converge

[John Naliboff]

Hi Wolfgang,

Thanks for that clarification.  

I’m still not exactly sure what such a large residual means in terms of the difference in the velocity field.  

However, I think the definition of the residual may be a bit different than what I’m used to:
	r = || v_i - v_i-1  ||  / || v_i  ||  
where v_i is the current velocities and v_i-1 are the previous values.

Cheers,
John

*************************************************
Assistant Project Scientist, CIG
Earth & Planetary Sciences Dept., UC Davis





> On Jun 6, 2016, at 11:25 AM, Wolfgang Bangerth <bangerth at tamu.edu> wrote:
> 
> On 06/06/2016 12:50 PM, John Naliboff wrote:
>> 
>> Ouch - The residual in the last step was 1.99733e+21.  Something is definitely
>> amiss ;)
> 
> John already asks all of the right questions, but I did wanted to comment on this: the residual is like a right hand side vector, which is an integral over cells. The mesh size here is around 1e5 meters, so the integral already has a factor of 1e15 just by the volume of each cell. Depending on what the average values of the integrand are, 1.997e21 may or may not actually be a large residual.
> 
> Ultimately, what matters is how it compares to the starting residual.
> 
> Best
> Wolfgang
> 
> 
> -- 
> ------------------------------------------------------------------------
> Wolfgang Bangerth               email:            bangerth at math.tamu.edu
>                                www: http://www.math.tamu.edu/~bangerth/
> 
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