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Nov 24, 2020 at 22:47 history edited RobPratt CC BY-SA 4.0
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Nov 24, 2020 at 21:42 comment added RobPratt I am using integer linear programming, which yields lower bounds via relaxation.
Nov 24, 2020 at 20:39 comment added Wolfgang ... But it seems tricky to capture what happens at the boundaries between two "zigzag parts". E.g. it makes sense to consider the cross at the right in your $10\times10$ loop as the union of 3 such zigzag parts (kind of direction changes), yet the straight segments are not between them, though at least 2 of the 3 are obviously required.
Nov 24, 2020 at 20:16 comment added Wolfgang Thank you for the $10\times14$ example, so for reasons of parity, $f(10,14)$ is $12$ or $14$. I had thought your program does some kind of exhaustive search. (BTW, how can you know it is bigger than $10$? - From the various examples, it is now obvious that a lower bound is given by the number of "zigzag parts" in the loop, as each "corner" between them needs at least one straight segment to link them without self-overlap). This argument shows that $f$ is not bounded, in fact it seems well possible that it yields $f(a,b)\ge\min(a,b)$.
Nov 24, 2020 at 17:11 history edited RobPratt CC BY-SA 4.0
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Nov 24, 2020 at 8:47 comment added Wolfgang Nice! Your $12\times12$ solution yields immediately $f(4a,2b)\le4a$ by cloning the 4 columns #3 to 6 (with then tweaking 3 segments to reproduce the inner $8\times4$ pattern to the left), which increases $f$ each time by $4$. $\quad$ What does your program yield for $10\times14$?
Nov 23, 2020 at 22:40 history edited RobPratt CC BY-SA 4.0
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Nov 20, 2020 at 1:57 history edited RobPratt CC BY-SA 4.0
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Nov 19, 2020 at 20:57 history answered RobPratt CC BY-SA 4.0