Hi Gerd, well setting initial search limit to 1000000 solves already loads of bad solutions and is still quite fast. Albeit using v 408 it was the best universal value I felt. Not much slower but in many cases getting better results. Going for much bigger initial value actually then caused also worse splits. I do not know how right now it determines the max value. but maybe increasing it would be good. And I feel it should increase/wait if the split obviously is not good. If it is good (all tiles except one within 80% of maxnodes) or very good (all except one 85%) it could stop earlier in order not to waste resources. I do not know how easy such a solution is to be implemented however. So far most bad splits are really realy bad (e.g. Norway 210 vs 135 tiles - in such cases a much longer time taken to find a good split is reasonable. Also as mkgmap will run faster if the split is better, compressing the maps will produce a smaller overall size if the split is better. On Thu, 1 Jul 2021 at 11:54, Ticker Berkin <rwb-mkgmap@jagit.co.uk> wrote:
Hi Gerd
Is this of any relevance -
https://en.wikipedia.org/wiki/Branch_and_bound
Ticker
On Wed, 2021-06-30 at 16:08 +0000, Gerd Petermann wrote:
Hi all,
I've started this branch to further improve the split results. Splitter has two different algorithms to find good splits. 1) Algo FULL tries first to split in the middle and then continues with the next positions (mid+1, mid-1, mid+2, mid-2, ...) The resulting parts are split again recursively. This should find the best possible split but can take very long when the only good split starts far from the middle.
2) Algo SOME uses some heuristics to test only some of the possible splits. This is typically much faster but sometimes doesn't find any solution and sometimes the FULL algo finds a better solution.
The trunk version tries first the one that is more promising and - if that fails to find a good split - tries the other. So, sometimes the FULL algo works for 2 minutes and then SOME finds a good result in a few seconds.
This branch executes both algorithms in parallel and uses the better result.
One of the open problems is to decide under what conditions the execution should stop. If the SOME algo finds a good solution within 20 secs should we still continue the FULL algo to find the best solution? If yes, how long? I'm playing with this, any input is welcome.
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