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Old April 10, 2011, 04:12   #1
Camcolit
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Spell Failure Rate Question

Hello everyone,

Just a quick question - I'm actually playing the Zangband tk variant but afaik the spell failure system is the same, maybe someone can confirm. My spell failure rate shows as the 5% minimum but I seem to fail a lot more than that. I get two failures in a row pretty often which is extremely unlikely at 5%. I'm not stunned or even in combat. Just randomly walking around the dungeon and I cast detect monsters and fail twice in a row. Any ideas? Thanks a lot.
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Old April 10, 2011, 05:23   #2
Zyphyr
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The RNG hates you. Don't take it personally though, it hates most people.
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Old April 10, 2011, 05:33   #3
Camcolit
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well it could be just bad luck, sure. It's natural to notice spells that fail a lot more than those that succeed. It's very hard to judge whether it's off or not, just seems that I've had a run of double-fails that's very improbable statistically if the rate is indeed 5%.
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Old April 10, 2011, 12:50   #4
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Well, after each time you have a failed spell, you have a 1 in 20 chance to fail again. You are probably casting lots of spells, so it would not be all that uncommon...
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Old April 10, 2011, 14:28   #5
Camcolit
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Well I play a vampire warrior-mage that is more warrior than mage at the moment, so I don't cast that much. Just wanted to find out if there was any hidden factor that increased spell failure that everyone knew about (except me). Now that I know there isn't I'll just chalk it up to the RNG - thanks
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Old April 11, 2011, 02:59   #6
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A couple of days ago I had a monumental sequence of Identifails at 33%. I'm quite used to six or more screw-ups, but this time I reckon I started counting at around 10-11 fails, and counted a further seven. Eighteen consecutive fails is a one in 38.7m chance (I've probably miscalculated).

I've also starved to death trying to satisfy hunger, having started spellcasting immediately I hit 'weak'.

I guess we don't remember to good rolls...
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Old April 11, 2011, 08:26   #7
zaimoni
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Quote:
Originally Posted by scud View Post
A couple of days ago I had a monumental sequence of Identifails at 33%. I'm quite used to six or more screw-ups, but this time I reckon I started counting at around 10-11 fails, and counted a further seven. Eighteen consecutive fails is a one in 38.7m chance (I've probably miscalculated).
Yes... (0.67)^18 ~ 0.074% i.e 1 in 1,351 chance for a theoretical uniform distribution.
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Old April 11, 2011, 08:40   #8
Timo Pietilä
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Quote:
Originally Posted by zaimoni View Post
Yes... (0.67)^18 ~ 0.074% i.e 1 in 1,351 chance for a theoretical uniform distribution.
If I understood correctly that would be 18 consecutive successes, not failures. Failures would be 0.33^18 ~= 2.154*10^-9 which is about 1 in 464246974
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Old April 11, 2011, 16:28   #9
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Except that the older rng, which I believe is the one Zangband has, has some issues. One failure seems to make successive failures likely. That's why they changed the RNG in Vanilla.So your initial failure rate may be 5%, but a failure will make a second one much more likely.
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Old April 11, 2011, 17:18   #10
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I don't know about "much". The RNG used in Vanilla now is slightly better than the old one, but it's not like the old one was bad. It compared decently well to the Mersenne Twister (I remember someone did a randomness study on the two awhile back). Yes, it's a bit prone to sequences of similar numbers, but IIRC not to the extent that you can blame every double-failure on it.
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