[Users] Test failures

[Frank Löffler]

On Thu, Nov 14, 2013 at 11:00:29AM +0100, Ian Hinder wrote:
> Why not before the release?  It is distracting to have certain tests
> which fail on some machines; since we know the reason for the
> failures, and there are other tests which test equivalent
> functionality, I think we should simplify the testing process and
> eliminate the Exact tests which are failing for which we have
> EinsteinExact versions.

I agree that this would be good, and was the intention when creating the
EinsteinExact tests. However, usually a change like this should be at
least mentioned on one of the calls and it's a bit late for that now
with the release in mind. If we will be not releasing this week (still
waiting for the hydro testsuites) and nobody speaks up here we can
remove them. Not all of the failing suites have an EE counterpart
though.

> > With some optimizations, such as -msse2 (Linux* OS) or /arch:SSE2
> > (Windows* OS),  the  compiler  may  change  floating-point  division
> > computations into multiplication by the reciprocal of the
> > denominator. For example,  A/B  is computed as A * (1/B) to improve
> > the speed of the computation.
> 
> I found this section of the manual page very confusing, but in the end
> interpreted it differently; i.e. that this would happen with
> -no-prec-div but not with -prec-div.  -prec-div is the default, and it
> would be very odd for the compiler to make these changes when
> -prec-div was set.  Can you try running one of the tests with
> -prec-div and with -no-prec-div to check which is being used?  There
> should also be a compiler option to output the effective flags that
> are being used.

> I think -xHost should be fine, and is probably the best way to choose
> the CPU-specific optimisations; I don't think it changes the numerical
> results (but compilers can always surprise us!).

I interpreted this exactly like you said you don't: -xHost might enable
sse2 and -msse2 might end up using inexact devisions, overwriting the
default of -prec-div.

Frank

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