Artifact rarities

[PowerWyrm]

This could be a tough question... any idea on how the Angband devteam came up with the values for artifact rarities?

Here's my problem... I'm maintaining a variant which has extra artifacts in artifact.txt, and I'm trying to figure out what value to put as rarity (or "commonness", as it is now) for those extra artifacts. Up to now, I was using some kind of formula based on the artifact price (per object_value), and it was somewhat in phase with the rarities of the base artifact set. With the new pricing system (per object_power), the results are not satisfactory at all...

Looking at the standard set of artifacts, some rarities seem really low compared to the intrinsic value of the item (body armor), some seem really high (cloaks). With the new pricing system, wouldn't it be easier to compute the rarity/commonness of an artifact directly from the artifact's "power"?

[jens]

I have no clue, but my belief is that somewhere long ago someone made a good initial setting of rarities. After that, people have changed rarities and added new artifacts, trying to get good results, and using feedback to tweak the values...

I'd say that the main problem with artifact rarities is that they are coupled with the rarity of the base object it is created from. This means that to get a certain rarity you need to adjust how rare the artifact is based on how rare the base item is...

I think there is a ticket for changing the coupling to base items, so all artifacts will be created in the same way as the 'special artifacts'. After that handling artifact rarities will become much simpler.

About your suggestion: It is good for most items, but I feel it adds some flavor in getting some artifacts at other rarities than the most balanced rarity for that object...

[Magnate]

This could be a tough question... any idea on how the Angband devteam came up with the values for artifact rarities?

Here's my problem... I'm maintaining a variant which has extra artifacts in artifact.txt, and I'm trying to figure out what value to put as rarity (or "commonness", as it is now) for those extra artifacts. Up to now, I was using some kind of formula based on the artifact price (per object_value), and it was somewhat in phase with the rarities of the base artifact set. With the new pricing system (per object_power), the results are not satisfactory at all...

Looking at the standard set of artifacts, some rarities seem really low compared to the intrinsic value of the item (body armor), some seem really high (cloaks). With the new pricing system, wouldn't it be easier to compute the rarity/commonness of an artifact directly from the artifact's "power"?

The original artifact rarities were chosen by the original authors - I don't know how much they changed between frog-knows and 2.9.x, but there has only been one major overhaul since then. That was in 3.1.1 when the old-style "1 in X" rarities got changed to alloc_prob, which is a percentage. At that point anything with rarity > 100 became alloc_prob 1, which IIRC was about half a dozen artifacts (Feanor used to be 120, Zarcuthra used to be 180, I forget the others).

The basic answer to your question is that it's not known what drove the original allocation of rarities. One could assume that being rational designers they attempted to make artifacts rare in proportion to their utility, but there are obvious exceptions like Thorin. My suspicion is that even the original coders did not really understand the outcomes of the code they had written (e.g. that Thorin is so common because small metal shields are so common).

My advice would be this: if you are adding deep, powerful artifacts, make them suitably rare (alloc_prob 1 for Ringil-like uber-arts, no more than 2 or 3 otherwise). If you are adding artifacts intended for use in the early game (like 'thancs and Paur* gauntlets), make them findable (alloc_prob between 10 and 50 depending on depth and base item type).

Once myshkin and I have finished the stats module, you'll be able to generate a couple of million dungeons and see whether your rarities are about right!

[PowerWyrm]

My advice would be this: if you are adding deep, powerful artifacts, make them suitably rare (alloc_prob 1 for Ringil-like uber-arts, no more than 2 or 3 otherwise). If you are adding artifacts intended for use in the early game (like 'thancs and Paur* gauntlets), make them findable (alloc_prob between 10 and 50 depending on depth and base item type).

Once myshkin and I have finished the stats module, you'll be able to generate a couple of million dungeons and see whether your rarities are about right!

The formula I currently use for artifact rarity is alloc_prob = 10000 / (object_value in kAU * base alloc_prob of item kind), limited between 1 and 100. Not perfect, but it seems to produce correct results.

The stats module seems a nice feature. Currently, I'm using the Dungeon Master in my variant (admin char that can travel between levels like a "ghost") to generate dungeon levels and see what artifacts are generated and their frequencies of generation. If I scum at 1000ft, I will generate an artifact every 20-30 levels. If I scum at 4000ft, I will generate multiple artifacts almost every level, due to pits and vaults. When GVs are generated (the GCVs and such), almost 20-30 artifacts are guaranteed to be generated (changing back the "8" spots to generate "excellent" items again didn't help). Killing unique monsters at that depth also produces multiple artifacts in many many cases. There was a time when killing Saruman was yielding 12 mixed weapons of slay foo... now the chance is more like getting 6-8 arts.