Talk:Psionics

Just had a thought on the formula!

What if the "Psionic Combat Strength" formula was a ' + ' rather than a ' * ' ?

It would mean the example Soldier would have a PCS of 111, rather than 1520, and the defending Muton would have:

Panic Chance = 76%
   MC Chance = 56%

These numbers seem more reasonable, don't you think?

--Danial 15:32, 19 Nov 2005 (PST)

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Right, it sounds much more reasonable now. My actual results were 1192 successes out of 2420 tries = 49.26% success rate. The MCer was right next to MC victim, and we know distance introduces some kind of decrease to base chance. That's the good news. The bad news is that I also tested psi str 95, skill 44 (and some higher skill levels) and never failed to MC once with these better MCers. Using your revision, a psi str 95, skill 44 guy should have had a success rate of 84% vs. a beginner Muton soldier (psi str 25, skill 0), not 100%. My higher-skill guys were also right next to their MC victims. So, to me the first example makes sense relative to your idea (fits base chance, plus a little distance adds a little more), but the second example counters it.

Still, it sounds WAY better than 1500% :)

I sure wish psi testing wasn't so labor intensive. I got those 2400 counts doing all that experience testing... not interested in doing it again, just for psi equations. At least not at the moment. :P ---MikeTheRed 21:12, 23 Nov 2005 (PST)

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Question: why is the Sectopod's psionic resistance listed as N/A? I've mind-controlled sectopods (or at least one square of a sectopod) on many occasions. I usually have it shoot itself, since it can target one of its other, non-MC'ed squares. From my anecdotal experience, their psi resistance seems somewhat high. --Papa Legba 14:19, 2 February 2006 (PST)

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Answer: If you look on the alien summaries in the wiki they all have a PSI resistance listed, except the Sectopod. Since it's not listed anyplace I put N/A. Feel free to put it where it belongs in the list if you have enough experience to feel comfortable ranking it. --Darksun

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Darksun, I took the liberty of signing your name for you, and making a separator line. Why not say a word about yourself under User:Darksun and also, use four dashes (----) to demarcate entries. For more on the basics of wiki'ing, see NKF's "Community Portal" at the bottom of the homepage. Past all that - welcome, fellow XCOMMIE! We were all wiki noobs once. But not everybody loves XCOM. You must. Welcome aboard!

Proceeding right along to flagellating, laugh - Where are you folks talking about Sectopod psi resistance being "N/A"? I see their Psi Strength as 100, and their Psi Skill as 0 at Beginner; Psi Strenth 116 and Skill still 0 at Superhuman. In this respect, they match Cyberdisks. What do you folks mean by Psi "resistance"? Do you know the math behind the psi equations? I haven't been able to figure it out. But the stats I just listed are ones hacked out of the game... Zombie is going to present a full precis' some time soon.

Great speaking at ya ... keep on contributing, Darksun!! --MikeTheRed

Alien psionic resistance

I haven't tried mind-controlling Cyberdiscs much, but if, as I've read elsewhere, both Sectopods and Cyberdiscs have have a Psi Strength of 100, they should probably both be classed "extremely high". --Ethereal Cereal 10:30, 4 May 2006 (PDT)

Psionic testing

I started doing some testing to figure out the psionics formula.

Initial finding: distance takes the hypotenuse into account. I'm not sure if the actual Pythagorean formula is used, but I can say this much: an Ethereal was able to panic a moderately-psi-weak soldier at 30 squares along the horizontal but not at 30 squares along the diagonal.

Second finding: the difference in "difficulty" between MC and panic is definitely 20 points (although that may not be percent). A soldier with 97 Psi strength, 0 Psi skill standing adjacent to an Ethereal Leader (60 str/45 skill) could not be panicked at all, but 96 Psi str could (often). The same soldier with 77 Psi str couldn't be mind-controlled, but could at 76 Psi str. With further testing, I see that 60/45 vs. 97 should succeed occasionally; I might retest this for greater precision, although the +20 still seems to hold.

Third finding: A soldier with 99 Psi str/0 skill could just barely be panicked by an adjacent Ethereal with 63/45. I couldn't count how often the Ethereal succeeded, but it was something like 1%-2% of the time. The same soldier was panicked just as infrequently by an Ethereal with 45/63 (str & skill reversed), and much more often by an Ethereal with 54/54. This pretty strongly suggests the attack portion of the formula involves psi str & skill multiplied together.

Data points collected so far:

• Ethereal, 63/45, just barely panicked soldier, 99/0
• Ethereal 40/40 just barely panicked soldier 75/0
• Ethereal 27/27 (multiplied together = 729) just barely panicked soldier 57/0
• Ethereal 10/73 (multiplied = 730) just barely panicked soldier 57/0
  • this confirms that attacking is based on str*skill
• Ethereal 18/18 just barely panicked soldier 49/0
• Ethereal 1/1 just barely panicked soldier 43/0
• Ethereal 1/1 just barely panicked soldier 1/210
  • this confirms Psi skill / 5 is used in calculating defense; 1 + (210/5) = 43

I also tested Ethereal 0/1 (no psi str, 1 pt. skill); it still attacked, but did not attack at 0 pts. skill no matter how high psi str was (no surprise there, otherwise all units would do psi attacks).

I ran the points through a curve-fitting program and got a nice and simple answer:

attack strength = psi str * psi skill / 50
defense strength = psi str + (psi skill / 5)

Panic Attack chance = 44% + attack strength - defense strength
Mind Control Attack chance = 24% + attack strength - defense strength

The formula has held up under limited further testing; I'm satisfied it's correct. I invite others to test it more than I have.

The impact of distance has yet to be tested, but it should be easy to figure out now.

--Ethereal Cereal 22:03, 26 May 2006 (PDT)

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There is a reasonable approximation to the Pythagorean formula (in the plane) that could have been used, that doesn't require loops or floating-point math:

max( | Δx | , | Δy | ) + ½min( | Δx | , | Δy | )

where Δ_ := _₂ - _₁.

It overestimates slightly. I haven't thought through how this would generalize to 3D. [Yanked from Moria, Angband, and variants...think it's too basic to copyright, though.]

One way to test whether the distance estimator is no greater than true Pythagorean formula by working out the greatest distance (pure x or pure y) that MC/Panic is not 0%, then testing on a diagonal with a "computed same". An integer-math overestimator (like the above) would by 0%.

Muliple of 5 allows replacing the diagonal with a suitably scaled 3-4-5 triangle...should work as well for testing.

--Zaimoni 2:38PM, 26 May 2006 (CDT)

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Wow... good approach to teasing this out, Ethereal!

Am I doing this right? I plugged in numbers for Muton, 25/0, Me 95/44, and got 83% MC Base Chance... But in much repeated testing (when learning about experience counters) it seemed quite solid that I was MC'ing him about half the time. Say 45-55% of the time. This was when right next to each other. Is 83% right for your equations?

Zaimoni, re: your equation, see Explosions#Distance_from_Ground_Zero. XCOM seems to use a fairly simple approach that doesn't involve Pythagoras per se. Since it's based on a very old engine, much of its stuff is integer based. Cool deal on the deltas and other wiki symbols - I wish I knew about them sooner! Actually I know where wiki symbol tables are... just didn't bother to look up so many symbols. :P

Nobody has tackled 3D distance yet, but I may soon, in studying illumination.

Once the equations are well known (maybe they are already), I imagine some cool 3D topographical graphs of the various factors (skill and strength, you vs. enemy) could be made. Do either of you have surface graph s/w at hand? All I've got at the moment is Excel. :(

Great work! Also thanks for cleaning up the page in general, Eth.

---MikeTheRed 22:24, 2 June 2006 (PDT)

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I suspect you've misremembered the details of your tests. The 49.26% success rate out of 2400 trials that you quote above would have been for your 95/16 soldier doing panics, not MCs: 44 + [95*16/50 = 30.4] - 25 = 49.4%, almost exactly the same as your 49.26%. A 95/44 doing panics would always succeed: 102.6%. A 95/44 doing MCs would succeed 82.6% of the time.

--Ethereal Cereal 11:06, 3 June 2006 (PDT)