[aspect-devel] Aspect 2.0 tests failure question

[Wolfgang Bangerth]

On 05/12/2018 12:27 AM, Rene Gassmoeller wrote:
> 
> let me add to this. I agree with Wolfgang that a relaxed tolerance would
> probably need to be around O(1), because we have test output that should
> be technically zero, but due to floating point imprecision, and due to
> the nature of the iterative solvers, is around 1e-18. The slightest
> change in iteration count can change this to 2e-18 or 0.5e-18, which
> technically is still zero, but drastically different from the reference
> result. Thus, I do not think a relaxed tolerance will be helpful.

That's not quite correct: we give numdiff both a relative and an absolute 
tolerance. Numbers are considered equal if they satisfy either of these 
criteria. I don't quite remember what the absolute tolerance is, but let's say 
it is 1e-6, then the numbers
   1.234e-9
and
   2.345e-11
are considered equal, even though their *relative* difference is quite large.

Best
  W.

-- 
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Wolfgang Bangerth          email:                 bangerth at colostate.edu
                            www: http://www.math.colostate.edu/~bangerth/