Talk:DrussGT

Just going through the algorithm, and I realised that there's a bug in my precise prediction: I'm using the bullet-hit-time of the 'target' point, not the point that I actually reach. This is left over from the days when the only thing my precise prediction checked was whether I could reach the target point. Now, for regular, constant distance surfing this is fine. But the moment I start changing distance my predictions can get a couple ticks off... Basically the less lateral velocity component I have, the more inaccurate my prediction gets. Which is bad against, say, RamBots, and in corner situations. I may have to rethink this algorithm... I've already tested doing an iterative search but it gets way too slow, way too quickly. --Skilgannon 10:47, 27 January 2009 (UTC)

Hi, I just want to know. You had once tell me that DrussGT doesn't call Math.random() in real battle, but it does in development process. Is the random call in development process use to generated all those 100 buffers' slices? Thanks » Nat | Talk » 06:02, 21 February 2009 (UTC)

Again, I'll rework DrussGT and see how it will act if it had 73,728 buffers. (The maximum buffer without duplicated buffer :)) » Nat | Talk » 06:05, 21 February 2009 (UTC)

• My robocode crash after intialize that bot with 73728 buffers! I think it too much :) » Nat | Talk » 07:18, 21 February 2009 (UTC)

Yes, it uses random() to decide which buffers to use, and which slices for those buffers (ie fine, regular, coarse). Unfortunately I couldn't do every possible buffer, due to memory constraints. So I use random() and make a set of buffers that hopefully covers all the segments fairly evenly. Also, if I used every possible combination I would probably run into problems with execution time while extracting buffers to use and smoothing new hits into the buffers. --Skilgannon 22:45, 21 February 2009 (UTC)

One more question: Does it do hit surfing? I go trough your code to understand the flattener (it easier to understand than Dookious one because my robot base on basic surfer, too.) I've recognize that you only do logHit() on hit and do logFlattener on every waves. Does hit surfer competitive? Or I miss something in your code? Thanks. » Nat | Talk » 02:21, 22 February 2009 (UTC)

Yes, hit surfing is the primary way of surfing. The flattener is only enabled against top guns. The reason for this is that if we are flattening the whole time, we can never learn where they are shooting, and dodge those areas. For example, against linear targeting, hit surfing can learn to dodge it perfectly, whereas flattener-only will still get hit. The same is also true against GF bots because they will learn that you move in certain ways, but the moment you get hit by them, you know how they think you move, so you can move differently. By rolling your surfing stats quickly you can stay ahead of their stats and actually do better than just creating a flat profile. Only against fast adapting guns is it necessary to enable the flattener. --Skilgannon 19:49, 22 February 2009 (UTC)

Question: Why you always use Float in DrussGT? Is it faster than Double? » Nat | Talk » 13:51, 6 March 2009 (UTC)

Yes, a float is significantly faster than double for multiplication/addition, which is what I use the most. It is slower for trig due to having to caste into a double, but with the new FastTrig class I can change that. It also uses half the memory. If I tried using doubles DrussGT would skip quite a few turns, and might also skip turns on initialisation due to allocating twice the memory. --Skilgannon 22:14, 6 March 2009 (UTC)

Well, I just decided to add "float" functionality to my FastTrig class. Iterestingly, despite the bulk of the calculation involved being multiplication/addition to get the index it isn't actually significantly different than the plain double version of FastTrig:

FastTrig init time: 0.00703 seconds
Wrost error: 0.000436324725
FastTrig time: 0.520 seconds
Math time: 8.811 seconds
Wrost float error: 0.000465920262
FastTrig float time: 0.510 seconds

The difference is slim enough that I don't think it's worth keeping two different versions. I'm just not sure which version to keep. But indeed, floats are nice for speed/memory and I'm already using them in a componant of my upcoming bot other than the FastTrig --Rednaxela 23:03, 6 March 2009 (UTC)

I don't think floats are faster than doubles at operation time, if I remember correctly calculations are done in higher precision registers anyway. The main time difference comes from the memory bus, a float(32-bits) can be read and written on a single memory access, while doubles(64-bit) are not. Some 64-bit architectures can move the whole 64 bit at once and have no real performance hit, while some use only 48 bit transfers, in those cases there is still a small difference. It's been a long time since I have read any of this, but I think that is the reason. --zyx 06:07, 7 March 2009 (UTC)

I'd say it really depends. For some applications before I've noticed as much as a 10% to 20% difference using floats, even with not being on a 64-bit architecture at all. Though for FastTrig float doesn't give a significant performance benefit. The reduced memory usage though, is of course undenyable. --Rednaxela 06:20, 7 March 2009 (UTC)

Well, the memory is of course half of it when using floats :). That can also affect on performance from the cache fetching point of view, and honestly most people doesn't need the extra precision that comes from using doubles. What I mean is that there isn't any real time performance difference that should people use float over double, if it is memory you need to optimize, float is the way. Otherwise I think people should use which ever he/she feels comfortable with. I use double when is a fresh new application just because doubles can represent all 32-bit integers exactly. And when I'm working with an API(like Robocode) I use the same as the API, that ensures that I will consistently behave the same as the API. I wouldn't consider it PrecisePrediction if it uses floats, because there will be differences when Robocode handles the same situations with doubles, I'd think of it as an approximation to it. When working on something as non-deterministic as a Robocode, maybe it's not even good to have more bits, but I'm a precision freak :/, that's why currently I'm using 628318 divisions on FastTrig --zyx 19:04, 8 March 2009 (UTC)

• Good point about the cache fetching. Also, as a precision freak, I take it you don't like VCS much ;P --Rednaxela 19:18, 8 March 2009 (UTC)
• Hehehe yes, I had been looking forward to making a DC bot for a long time, but I admit that VCS is a very good technique and certainly was easier to learn the heavy stuff of GF and WS using simple VCS. -- zyx