# Coordinating Variable Signs

Someone asked me today (or yesterday, depending on whose time zone you go by) how to force a group of variables in an optimization model to take the same sign (all nonpositive or all nonnegative). Assuming that all the variables are bounded, you just need one new binary variable and a few constraints. Assume that …

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# Sniffing out pandas’ social secrets

I find I tend to write most of my blog posts from the field – I guess this is what I think readers will find most exciting, which is probably because it’s what I find most exciting. I thought that I was done with fieldwork back in April, but while doing analyses for my dissertation …

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# The French Way: Alain Connes interview

I came across this interview with Fields Medalist Alain Connes (excerpt below) via an essay by Dominic Cummings (see his blog here). Dom’s essay is also highly recommended. He has spent considerable effort to understand the history of highly effective scientific / research organizations. There is a good chance that his insights will someday be put …

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# Choosing “Big M” Values

I seem to bring up “big M” models a lot, so apologies if I end up repeating myself in places here. Not long ago, someone passed along highlights of a “big M” type model to me and asked if he could somehow reformulate to get rid of $$M$$. I did not see any good way …

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# Adding Items to a Sequence

A question posed on OR-Exchange in 2017 asked the following: Given a tour of nodes, how does one best add two new nodes while respecting the ordering of the original tour. Specifically, the author began with a tour 0 – 1 – 2 – 4 – 6 – 0 (where node 0 is a depot) …

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# NP Confusion

I just finished reading a somewhat provocative article on the CIO website, titled “10 reasons to ignore computer science degrees” (when hiring programmers). While I’m not in the business of hiring coders (although I recent was hired as a “student programmer” on a grant — the Universe has a sense of humor), I find myself …

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# Scientists of Stature

The link below is to the published version of the paper we posted on biorxiv in late 2017 (see blog discussion). Our results have since been replicated by several groups in academia and in Silicon Valley. Biorxiv article metrics: abstract views 31k, paper downloads 6k. Not bad! Perhaps that means the community understands now that genomic …

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