[petsc-dev] New ILU, associativity changes

Hong Zhang hzhang at mcs.anl.gov
Wed Feb 24 08:58:58 CST 2010


Can you simply your test into a small petsc example that repeats
this behavior?
I want test it myself to make sure the differences are not
result of bug in the new implementation.


On Feb 24, 2010, at 2:55 AM, Jed Brown wrote:

> I notice low-bit differences between the new ILU and versions from  
> last
> month.  From one of my tests:
>  -Algebraic residual        |x|_1 9.35e-16  |x|_2 2.59e-16  |x|_inf  
> 1.67e-16
>  +Algebraic residual        |x|_1 1.09e-15  |x|_2 3.00e-16  |x|_inf  
> 1.67e-16
>  -Algebraic residual        |x|_1 6.18e-12  |x|_2 2.59e-13  |x|_inf  
> 4.08e-14
>  +Algebraic residual        |x|_1 6.19e-12  |x|_2 2.59e-13  |x|_inf  
> 4.08e-14
>  -Algebraic residual        |x|_1 4.85e-12  |x|_2 1.95e-13  |x|_inf  
> 4.73e-14
>  +Algebraic residual        |x|_1 4.84e-12  |x|_2 1.95e-13  |x|_inf  
> 4.73e-14
>  -Algebraic residual        |x|_1 3.36e-13  |x|_2 1.56e-14  |x|_inf  
> 3.06e-15
>  +Algebraic residual        |x|_1 3.32e-13  |x|_2 1.54e-14  |x|_inf  
> 3.05e-15
> I'm guessing this comes from traversing rows in the other order during
> backsolve.  This is no problem at all since both are equally valid, I
> just wanted to note that some rounding effects are visible.
> Jed

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