Off the top of my head, the only the I can see is it would be nice to be
able to sum the error vector to get the total error estimate. But maybe
there's other things already there to do that?
On Thu, Oct 11, 2012 at 11:45 AM, Roy Stogner <royst...@ices.utexas.edu>wrote:
>
> Vikram and I are waffling on this question, so I thought I'd throw it
> out for everybody's feedback:
>
> For signed error estimates, e.g. estimates of Quantity-of-Interest
> error where Q - Q_h ~= sum_E ( \eta_E ), what should the
> estimate_error() method put in our ErrorVector? The signed eta_E,
> or the unsigned abs(eta_E)?
>
> On the one hand: if error vectors can contain signed values, then
> every MeshRefinement heuristic is going to have to be modified to do
> abs() calls itself, 99% of the time this is going to be a complete
> waste, and (given that the ErrorEstimator subclass also calculates a
> global "Q - Q_h" estimate that can be accessed without that
> summation) it's hard to come up with usage cases for the signed local
> values.
>
> On the other hand: since abs() doesn't require any more cache misses
> or use any more memory bandwidth, doing it redundantly in
> MeshRefinement local variables may not actually waste time on modern
> processors. And if someone ever *does* want to use signed local
> values for something (cancellation-aware refinement heuristics??) then
> it would be good if we didn't destroy that sign information before
> giving local values to them.
>
> Opinions, or factors I've missed?
> ---
> Roy
>
>
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