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From: Mark Friedenbach <mark@friedenbach.org>
To: Gary Mulder <flyingkiwiguy@gmail.com>
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Subject: Re: [bitcoin-dev] Block size following technological growth
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The median is used here because that is the consensus rule -- a block
cannot have a timestamp older than the median time of the last 11 blocks.
By linking the changeover to this rule we avoid perverse incentives about
miners lying in their timestamps, or the threshold being crossed, then
reverted, then crossed again, etc.
Maybe a different percentile would have been a better choice, but that ship
sailed in 2009. The rule is what it is right now, and we benefit the most
from using the same rule as consensus for the threshold.
On Jul 30, 2015 9:57 AM, "Gary Mulder via bitcoin-dev" <
bitcoin-dev@lists.linuxfoundation.org> wrote:
> On 30 July 2015 at 16:12, Jorge Tim=C3=B3n <
> bitcoin-dev@lists.linuxfoundation.org> wrote:
>
>> 1) Unlike previous blocksize hardfork proposals, this uses median time
>> instead of block.nTime for activation. I like that more but my
>> preference is still using height for everything. But that discussion
>> is not specific to this proposal, so it's better if we discuss that
>> for all of them here:
>>
>> http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2015-July/009731.=
html
>
>
> Note that a "median" is a special case of a 50% percentile. If you desire
> to apply a more stringent criteria you can use the 75th or even 90th
> percentile.
>
> https://en.wikipedia.org/wiki/Percentile
>
> Perhaps if a statistician (i.e. not me) could be found to offer her
> services, she could become a resource for helping selecting the most
> appropriate statistical algorithms on request (and implemented Integer ma=
th
> as per Gavin, from memory), considering the consequences of learning
> post-fork that a "bad statistical model" was chosen.
>
> e.g. an exponentially weighted moving average is usually much less
> volatile and harder to manipulate than a simple moving average, but still
> can "respond" to short term drivers.
>
> Regards,
> Gary
>
> _______________________________________________
> bitcoin-dev mailing list
> bitcoin-dev@lists.linuxfoundation.org
> https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev
>
>
--001a113eb9c88552a1051c1ad18e
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<p dir=3D"ltr">The median is used here because that is the consensus rule -=
- a block cannot have a timestamp older than the median time of the last 11=
blocks. By linking the changeover to this rule we avoid perverse incentive=
s about miners lying in their timestamps, or the threshold being crossed, t=
hen reverted, then crossed again, etc.</p>
<p dir=3D"ltr">Maybe a different percentile would have been a better choice=
, but that ship sailed in 2009. The rule is what it is right now, and we be=
nefit the most from using the same rule as consensus for the threshold.</p>
<div class=3D"gmail_quote">On Jul 30, 2015 9:57 AM, "Gary Mulder via b=
itcoin-dev" <<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.or=
g">bitcoin-dev@lists.linuxfoundation.org</a>> wrote:<br type=3D"attribut=
ion"><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-le=
ft:1px #ccc solid;padding-left:1ex"><div dir=3D"ltr"><div class=3D"gmail_ex=
tra"><span style=3D"font-size:12.8000001907349px">On 30 July 2015 at 16:12,=
Jorge Tim=C3=B3n=C2=A0</span><span dir=3D"ltr" style=3D"font-size:12.80000=
01907349px"><<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org" ta=
rget=3D"_blank">bitcoin-dev@lists.linuxfoundation.org</a>></span><span s=
tyle=3D"font-size:12.8000001907349px">=C2=A0wrote:</span><br style=3D"font-=
size:12.8000001907349px"><blockquote class=3D"gmail_quote" style=3D"font-si=
ze:12.8000001907349px;margin:0px 0px 0px 0.8ex;border-left-width:1px;border=
-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex">1) U=
nlike previous blocksize hardfork proposals, this uses median time<br>inste=
ad of block.nTime for activation. I like that more but my<br>preference is =
still using height for everything. But that discussion<br>is not specific t=
o this proposal, so it's better if we discuss that<br>for all of them h=
ere:<br><a href=3D"http://lists.linuxfoundation.org/pipermail/bitcoin-dev/2=
015-July/009731.html" rel=3D"noreferrer" target=3D"_blank">http://lists.lin=
uxfoundation.org/pipermail/bitcoin-dev/2015-July/009731.html</a></blockquot=
e><div style=3D"font-size:12.8000001907349px"><br></div><div style=3D"font-=
size:12.8000001907349px">Note that a "median" is a special case o=
f a 50% percentile. If you desire to apply a more stringent criteria you ca=
n use the 75th or even 90th percentile.</div><div style=3D"font-size:12.800=
0001907349px"><br></div><div style=3D"font-size:12.8000001907349px"><a href=
=3D"https://en.wikipedia.org/wiki/Percentile" target=3D"_blank">https://en.=
wikipedia.org/wiki/Percentile</a><br></div><div style=3D"font-size:12.80000=
01907349px"><br></div><div style=3D"font-size:12.8000001907349px">Perhaps i=
f a statistician (i.e. not me) could be found to offer her services, she co=
uld become a resource for helping selecting the most appropriate statistica=
l algorithms on request (and implemented Integer math as per Gavin, from me=
mory), considering the consequences of learning post-fork that a "bad =
statistical model" was chosen.</div><div style=3D"font-size:12.8000001=
907349px"><br></div><div style=3D"font-size:12.8000001907349px">e.g. an exp=
onentially weighted moving average is usually much less volatile and harder=
to manipulate than a simple moving average, but still can "respond&qu=
ot; to short term drivers.=C2=A0</div><div style=3D"font-size:12.8000001907=
349px"><br></div><div style=3D"font-size:12.8000001907349px">Regards,</div>=
<div style=3D"font-size:12.8000001907349px">Gary</div></div></div>
<br>_______________________________________________<br>
bitcoin-dev mailing list<br>
<a href=3D"mailto:bitcoin-dev@lists.linuxfoundation.org">bitcoin-dev@lists.=
linuxfoundation.org</a><br>
<a href=3D"https://lists.linuxfoundation.org/mailman/listinfo/bitcoin-dev" =
rel=3D"noreferrer" target=3D"_blank">https://lists.linuxfoundation.org/mail=
man/listinfo/bitcoin-dev</a><br>
<br></blockquote></div>
--001a113eb9c88552a1051c1ad18e--
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