Re: Work unit age

Martin wrote:

Robi wrote:

Martin wrote:

Stratcat� wrote:
[...]

do, but I'm assuming for WU's to be corroborative, they'd have to be
consistent within a reasonably narrow window of deviation.


The returned results are compared for an EXACT match. The results must
be IDENTICAL, otherwise there must have been a computational error.


Sorry, but no.
With the fft algorythms there are "rounding" errors which differ
from processor to processor (and OS? not sure here).

[...]

Yes...? Please explain further...

(Big hint: Have a look at where the rounding errors are. Note that
numbers for the results will be deliberately rounded for the analysis! (:-))


ok, not fft rounding errors:
http://setiathome.ssl.berkeley.edu/newsletters/newsletter8.html

"There are several reasons why a result returned by a SETI@home volunteer
 might be incorrect. The most common reason we get incorrect results is
 processor malfunction. If a processor overheats, perhaps because there is
 dust buildup inside the machine, or maybe it's just a really hot day, the
 first part of the chip to fail will be the most complex part, the floating-
 point unit. A failure of the floating-point unit, which is responsible for
 most of the calculations performed by SETI@home, will usually not cause a
 computer to crash. It will cause the computer to generate incorrect results.
 These innocent failures are responsible for most of the incorrect results
 we see. The most common symptom of this problem is that every result from
 malfunctioning computer contains hundreds of potential signals. Of course,
 some valid results also contain hundreds of signals."

The only room for variation is for exactly where in the analysis a WU is
abandoned due to RFI. The whole result is discarded then in any case,
other than for marking that WU as unusable.


I honestly doubt that. Agreed, the analysis is stopped, but only due to
an overflow of data. That doesn't mean that the WU is useless (or unusable
as you put it).


On what basis?...


"There are also many work units that were processed by more than one
 version of the SETI@home client. More recent versions include analysis
 that was not present in the early versions, so certain signals will
 only be found with new versions"

IOW, a more advanced client could identify RFI and filter it out, catching
a signal in the background. Of course, such a client would first have to
be designed, but it shows that even if a WU has RFI it doesn't mean it is
useless.


--
Robi
(2.7#@ 2.62 yrs)