Use a better algorithm for magic devices fail rate

[takkaria]

An idea might be to plot the existing rates on a graph of player level vs item level first.

[takkaria]

Oh, and display it in item descriptions too.

[magnate]

​http://angband.oook.cz/forum/showthread.php?t=1222

[magnate]

New discussion here: ​http://angband.oook.cz/forum/showthread.php?t=1957

My next job is to create a list of all activatable devices/effects together with their depth (which is currently their difficulty rating), assign putative difficulty ratings, and list the base device skill of each race/class combo at each clev. That should enable a fairly easy attempt at a new algorithm. I feel a spreadsheet coming on.

[magnate]

The spreadsheet is at ​http://www.terminalarrogance.com/devices.xls, but neither of the algorithms is satisfactory. High level magi are too good, and high level warriors are not good enough - so I think this means we need a quadratic approach. Postponing to 3.1.2 as agreed with Takkaria.

[magnate]

From #angband-dev for posterity:

(17:28:46) takkaria: I think I'd be happy capping at 1 or 2% fail instead
...
(20:42:37) takkaria: yeah, since AIUI, activation is basically a mechanical or thought based process
(20:42:53) Magnate: So no effect from wounds or blindness, small for poison, fear, berserk, and slightly more for stunning then confusion at the top. Ok?
(20:44:28) takkaria: yeah, I think that works

(with small positive effects from Bless and Heroism, and max fail of 95%)

[magnate]

(in the same conversation it was agreed that confusion should increase min fail to no more than 25% - though of course this does not help with aiming)

[magnate]

[fed2198] (SVN r1817)