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invictius

Killing imps with one shotgun blast

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I read somewhere that there's a 3 in 20 chance of killing an imp with one shotgun shot, if all seven pellets hit. Now, take that and consider one of those situations where if you flipped a coin 100 times, it only has a x.xxxxxx% chance of coming up heaps 100 times. Would someone with a lot of time on their hands like to line up 100 imps and keep re-trying putting them each down in one hit? Or perhaps screwing around with the fact that these things are randomized and doing something awesome in a level that depends heavily on the random number generator.

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TimeOfDeath said:

100imps.wad

I don't think that's right. Went through the map once and killed 94/100 imps with one shot.


Yeah, because one run is totally statistically significant. Plus, to conduct a proper test, each imp should be in its own cubicle, individually shot and isolated so that any extra pellets don't go hit other imps, fouling the results.

Edit: In a previous life, I had done much more thorough analysis of the RNG, and had computed an about 86.5% figure, hence the roughly 3/20 change. There's also a 94% figure mentioned along with it, but that can only occur by changing the Imp's Thing properties with DEHACKED (some properties affect damage calculations), but not in normal gameplay vs standard monsters.

ToD just got a figure close to the 94% (unfeasible on vanilla) statistical average on the first run by pure luck. Still, if serious testing is to be done, the map should be redesigned (or aiming at each imp very carefully).

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Well, invictius said 3/20 chance of killing an imp with one shotgun shot, so I figured the one test I did of 18.8/20 chance was telling enough. But I guess he meant to say 3/20 chance of NOT killing an imp with one shotgun shot?

My first test was in prboom-plus and I did make sure that no extra pellets hit other imps (I stood right in front an imp and shot, then strafed to the next, etc). I did a second test in vanilla and killed 96/100 with one shot.

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I tried ToD's testmap, got 98/100 in pr+ with cl2. I feel that a mathematical average below 90% means just an error in the computations.

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TimeOfDeath said:

But I guess he meant to say 3/20 chance of NOT killing an imp with one shotgun shot?


Yeah, this makes a lot more sense. I was gonna say, usual experience, pretty easy to kill an imp in one blast, but won't about 1/10 of the time. Just common enough to feel annoying.

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Magnusblitz said:

Yeah, this makes a lot more sense. I was gonna say, usual experience, pretty easy to kill an imp in one blast, but won't about 1/10 of the time. Just common enough to feel annoying.


I'm not sure what exactly the figure was. It was in a very recent thread that started talking about how useful the shotgun is.

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TimeOfDeath said:

Well, invictius said 3/20 chance of killing an imp with one shotgun shot, so I figured the one test I did of 18.8/20 chance was telling enough. But I guess he meant to say 3/20 chance of NOT killing an imp with one shotgun shot?


*facepalm* Yes, you're right. I didn't notice this either until you pointed it now. The 3/20 chance is that of NOT killing it in one shotgun shot. There would be something wrong if the chances were this reversed...

Trivia: there's about a 4/256 chance of KILLING a Lost Soul with 1 shotgun blast (about 2.5%).

And again, when making those tests, care must be taken that the extra pellets are NOT absorbed by other imps. Good for combat, but not for experiments ;-)

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The exact information is on the doom wiki if you loom up the shotgun. Iirc the damage done by a shotgun if all 7 pellets hit can be anywhere between 35 and 115 damage in increments of 5.

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35 and 105 to be exact, if you assume a simplistic "7 pellets with damage of 5, 10 or 15 each", but the Doom RNG doesn't allow for a sequence of random numbers leading to 7 straight 15s in a row - but it's possible to get exactly 100 damage.

The wiki's calculations are based on the simplistic assumpionsm, which work well enough but make borderline cases appear more probable than they really are, and they don't take into account code intricacies.

My shotgun anal-ysis is based on careful emulation and study of the RNG's actual values and the exact number of times it's called when doing an action such as shooting (e.g. 1 shotgun pellet or pistol shot needs at least 3 consecutive RNG values to be read, but may require up to 10 in the most general case).

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To clear this mess up, I think this is where the equivocation originated. And yet I stated it clearly:

Maes said:

The imps are really the workhorse of Doom monsters: not too tough to be just annoying meat shields, but not so weak as to go down too easily as zombiemen do. They are pretty much the reason for seeking out a shotgun ASAP, and even with it, there's about a 3/20 chance that they'll survive even a full-face, perfect SG blast to the face.

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Well how often can you kill a pinky with 2 blasts? Every time I pull that one off I feel pretty special. Although it is pretty much always with the ssg which uses 2 shells also so I guess I'm talking ult. Doom.

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It's pretty odd that everyone gives Doom's random number generator -- really a static array by my understanding -- so much flack. While it does only pull the same numbers over in a continuous list, it effectively prohibits someone from getting redundant or near redundant values one right after the other, making the gameplay feel very natural and reasonably predictable. ZDoom or any soureport with a true pseudo-random number generator just feels awkward by comparison.

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From point-blank distance, it's not a problem. But as has been mentioned, it's all basically up to the (pseudo-)random generator. And especially with the shotgun, which fires multiple pellets that spread across a specific angle, killing imps with a single blast from longer distances gets harder.

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Maes said:

And again, when making those tests, care must be taken that the extra pellets are NOT absorbed by other imps. Good for combat, but not for experiments ;-)


Usually you're fighting with more than one imp in view, so in practise with careful aligning of shotgun shots you increase your chances of killing imps in one sg shot. Even if one survives the full shot, the second shot will usually take out two imps close to each other.

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