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Lower bounding w_min to 1 instead of 0? #416

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ksahlin opened this issue Apr 18, 2024 · 0 comments
Open

Lower bounding w_min to 1 instead of 0? #416

ksahlin opened this issue Apr 18, 2024 · 0 comments

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@ksahlin
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ksahlin commented Apr 18, 2024

For logging and coming back to later:

Currently, we have randstrobe(l, u, q, max_dist, std::max(0, k / (k - s + 1) + l), k / (k - s + 1) + u).

This is is primarily for our parameter optimization, but if parameters is chosen such that k / (k - s + 1) + l <= 0, then w_min is set to 0. Because of our link function std::bitset<64> b = (strobe1.hash ^ syncmers[i].hash) & q;, w_min= 0 will deterministically pick strobe1=strobe2 and thus effectively emulate k-mers. For such a setting and some read lengths, I observed a significant drop in map rate (over 5%), increased runtime, and often but not always a decrease in accuracy. This may have been the problem with our initial parameter optimization?

With mcs, picking k-mers (w_min=0) should be strictly worse than any other parameters, since we get the k-mers for free.

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