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Does MF decrease the probability of dropping normal items ?

Discussion in 'Theorycrafting and Statistics' started by Zephyrin, Jun 23, 2005.

  1. Zephyrin

    Zephyrin IncGamers Member

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    Does MF decrease the probability of dropping normal items ?

    According to ATMA, it doesn't.

    Although usually I 100% believe ATMA, this time I have some doubt:

    I thought that a dropped magic or rare item, or unique, with not enough MF to trigger a magic/rare (or set/unique etc.) drop, would have been normal.

    So it seems to me, but I could be wrong, that the residual probability of dropping a normal with a high MF should be the probability of dropping it with zero MF, diminished by the sum of probabilities of dropping a magic/rare etc. caused by the high MF. Maybe it is marginal only, but the numbers are strictly identical in ATMA (I compared them for Archon Plate, but it should be the same for all items, I guess).

    Also there is an apparent feeling, when in game, that more normal (or socketed) items drop with little MF than with high MF. But this could just be an appearance, due to the little or no blue/yellow items dropping with no MF.

    Any idea or correct theory to contradict the views above ?
     
  2. Myrakh-2

    Myrakh-2 IncGamers Member

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    If by "normal" you mean "not exceptional or elite" then MF has no effect.

    If by "normal" you mean white/grey then yes, MF certainly reduces the number of "normal" items since it makes more items turn magic (or better).
     
  3. Thrugg

    Thrugg IncGamers Member

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    I think you have misunderstood Atma, and I agree it could be a little clearer.
    as far as I can see, Atma does not ever give you odds of a non-magical item dropping. It gives you Unique, Set, Rare, Magic or Base Item. Base Item means "an Archon Plate of any kind", not "a non-magic Archon Plate".

    MF will of course not affect the chance of an Archon Plate dropping, but will as you expect reduce the chance of a non-magic one dropping.

    Atma was originally written for people interested in Unique and Set items, and correctly calculating non-magicals was not a prioirty feature. I should be straightforward to add, so it might go on the list for the next revision. Also of interest would be the chance of Superior and even Low Quality (for those ilvl 1 socketers). They are also determined in the MF phase (even though they are not affected by your MF, ironically).
     
  4. helvete

    helvete IncGamers Member

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    :clap: ATMA revise!! ATMA revise!! And please include drop calculating chests in the budget! :clap:
     
  5. Myrakh-2

    Myrakh-2 IncGamers Member

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    And separate the drop calculator out of the rest of the app --- I always find it a bit stupid to have to go to the submenu of a submenu to get to the only interesting part of the thing :)

    Especially since the drop calculator doesn't really have anything to do with the single player char editing stuff.
     
  6. Zephyrin

    Zephyrin IncGamers Member

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    :clap: I concur :clap:

    Also to Myrakh's idea to separate the drop calculator from the rest of the application.

    @ Thrugg, thanks for the clarification. btw, base item is truly misleading. It is more a "base probability" than a "base item probability".

    Another question: is there a simple formula to determine the probability to drop a superior quality item (derived from the base item drop probability) ? Same question for socketed items, but I guess it is more complex here because the ilvl is necessarily involved, since it conditions the max number of sockets.
     
  7. Pherdnut

    Pherdnut IncGamers Member

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    If you understand the basics of MF that part should be reasonably clear. Just take white item drop odds for what they would be with 0 MF.
     
  8. Thrugg

    Thrugg IncGamers Member

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    Atma is a Single Player tool which you online guys get to make use of, don't ever expect it to neglect its SP roots :)

    The drop calc requires all the same text files that the item display does; I agree they could be installed as separate apps in the same directory, but it seems inefficient to have separate installers that both contain 90% the same stuff. Still, the Doc reads all these threads eventually so he may consider it...

    You can't edit SP chars with it, btw, you can only move items around. That is an important distinction.

    Zeph, the MF calculation routine doesn't stop at Magic, it just stops using your MF at Magic. If an item fails to be Unique>Set>Rare>Magic it next tries to be Superior. The same formula is used except omitting the MF step and the Cap step and the boss bonus step (which is most of the steps :)). In 1.10 there is a HiQuality base of 12 and a divisor of 8 (9 and 8 for class specifics) - these values are stored in itemratio.txt. That means that we take the item level and the base item qlvl and work out the following:
    Chance = 12 - [(ilvl - qlvl)/8], rounded down.
    Odds of Superior = 1/Chance.

    So if you kill one of Pindle's minions (mlvl 86) and they drop you a Berserker Axe (qlvl 85) you have a 1 in (12 - (86-85)/8 = 12) chance of it being Superior. But if the same monster drops you a Short Sword (qlvl 1), you have a 1 in (12 - (86-1)/8 = 2) chance, but only if it gets past all the checks for being magic or better first.

    There is even one more check, if it fails to be Superior there is a further check for normal quality, ie plain white. Here the numbers are actually different between normal difficulty and the other two (and why you see more low quality items in normal) - 2 and 2 for normal and 1 and 1 for NM/Hell. 1 and 1 means that there is a 1 in 1, 100% base chance of an item being normal quality - so the only way to get a low quality one is by getting a monster to drop an item with qlvl > mlvl. Then the modifier works in reverse. But, it is an unusual occurrence. In the Pit for example, regular monsters are mlvl 85, and the only item type with qlvl > 85 is Unearthed Wand, so that is the only item that can drop low quality in the Pit. However, go to Hell Cows where the monsters are all only mlvl 81 but can still drop TC87 with its qlvl 85s, and the white TC87 items you'll find will have a lot more low quality in them.

    I actually don't know the exact odds on an item getting sockets. It doesn't appear to be in any of the text files I am familiar with. I believe it is around 1/3, provided the item is sup or normal quality (can't get socketed low quality). Maybe RTB knows...
     
  9. Zephyrin

    Zephyrin IncGamers Member

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    Thrugg, just to say that once in my lifetime Iwas able to contradict you without mistake ;) :
    12 - (86-85)/8 = 11 if rounded down.

    Edit: I'm not even sure of that... do you mean truncated (down) or rounded to the nearest integer value, with the rule of selecting the down value in case of two possible choices ?
    in other words,
    12 - 0.125 = 11.875 truncated to 11
    or rounded to 12 because 11.875 > 11.5 ?
    Of course this doesn't matter at all for me in the game, but it matters in my permanent quest for accuracy.

    Apart from this, all I can say is :worship:
     
  10. Thrugg

    Thrugg IncGamers Member

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    Sorry, yes I was unclear.
    Diablo is entirely programmed in integers although it does cheat occasionally by storing 128 or 256 times the number it really uses, to get greater accuracy.

    As a result it always rounds divisions down (integer division, 7/2 = 3).
    However, that means it rounds down as part of the division, before the divided number gets used elsewhere.

    So, 12 - [(86-85)/8] = 12 - [1/8] = 12 - 0 = 12.

    Because the division is later subtracted, the whole equation does end up being effectively rounded up.
    We usually highlight this kind of rounding with square brackets.
     
  11. RTB

    RTB IncGamers Member

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    Yeah, hardcoded as expected. I vaguely remember a chance of 20%.
     
  12. TheJarulf

    TheJarulf Banned

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    Correct. Although I have a small recollection that it might be 21% instead of 20% due to checking for <= 20 instead of <20 (on a random[100] roll). There are a few such odd checks in the game here and there.

    Also note that a set and low quality item can't get sockets. Nor can any item that got any form of "indestructable" modifier or one that got no durability (like jewlery).
     
  13. Myrakh-2

    Myrakh-2 IncGamers Member

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    So how come bows can get sockets?
     
  14. krischan

    krischan Europe Trade Moderator

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    I guess you meant it like this, but just to make it clear for the others: Only normal and superior items can get sockets as a kind of "free" mod with a 20% chance upon item generation. Cracked items can't get them when they drop. Magicals, rares and crafted items can get them from an affix. Uniques and set items get them as a part of their builtin features.

    Regarding indestrucible items: I guess you meant something completely different :lol:
     
  15. TheJarulf

    TheJarulf Banned

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    Ehhh, oops, I think I messed up two things!!! I was thinking of etheral, not sockets. Disregard my comment above! This should apply to the chance for "sockets" as well, also thinking about ethereal! Sorry!!

    It is too late to edit my message above though.
     
  16. TheJarulf

    TheJarulf Banned

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    I made a quick check and found a 33% chance for sockets. Does that seem right for items that can get sockets randomly? In the same code there seemed to be a cap on 3 sockets for normal difficulty, 4 for nightmare and 6 for hell (in addition to other caps for item types that is in another part of the code that actually determin the number of sockets). There was also a check for version 0 items that appearantly has the cap set to 3 (2 for type "25" items, have not checked what it is).

    Also, low quality items is excluded in this code from sockets, as is stackable items. IN addition it checks for a non 0 value in "gemsockets" data.

    Sorry if some of the above is technical and hard to understand without looking at data files.
     
  17. jiansonz

    jiansonz IncGamers Member

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    Yep, this is all in line with my experiences of the game. I often shop socketed items in the first two acts in Normal, and the non-magical ones do seem to have sockets about 1/3 of the time.
     

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