R v. Python

A couple of days ago, I was having a conversation with someone that touched on the curriculum for a masters program in analytics. One thing that struck me was requirement of one semester each of R and Python programming. On the one hand, I can see a couple of reasons for requiring both: some jobs …

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A Java Container for Parameters

A few days ago, I posted about a Swing class (and supporting stuff) that I developed to facilitate my own computations research, and which I have now made open-source in a Bitbucket repository. I finally got around to cleaning up another Java utility class I wrote, and which I use regularly in experiments. I call …

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Indicator Constraints v. Big M

Way, way back I did a couple of posts related to how to model “logical indicators” (true/false values that control enforcement of constraints): Logical Indicators in Mathematical Program Indicator Implies Relation The topic ties in to the general issue of “big M” model formulations. Somewhere around version 10, CPLEX introduced what they call indicator constraints, …

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Naming CPLEX Objects

A CPLEX user recently asked the following question on a user forum: “Is there a way to print the constraints as interpreted by CPLEX immediately after adding these constraints using addEq, addLe etc.” The context for a question like this is often an attempt to debug either a model or the code creating the model. …

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How to Crash CPLEX

A question elsewhere on the blog reminded me that some users of the CPLEX programming APIs are not conscious of a “technicality” that, when violated, might cause CPLEX to crash (or at least throw an exception). The bottom line can be stated easily enough: modifying a CPLEX model while solving it is a Bozo no-no. …

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Failures to Listen

One year ago today, Rachael Denhollander addressed the Ingham County court in Michigan, her abuser, and the institutions that failed to protect her and her #SisterSurvivors. Listen again to part of what she said on January 24, 2018: This is what it looks like when institutions create a culture where a predator can flourish unafraid and …

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Guessing Pareto Solutions: A Test

In yesterday’s post, I described a simple multiple-criterion decision problem (binary decisions, no constraints), and suggested a possible way to identify a portion of the Pareto frontier using what amounts to guesswork: randomly generate weights; use them to combine the multiple criteria into a single objective function; optimize that (trivial); repeat ad nauseam. I ran …

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Two Books – Real Gifts

I have a pile of about 10 books I’m wading through, but two are of special note as I write this. As I noted in my last blog of 2017 I have the privilege of reading, and especially of reading books. For the past few years I’ve read on average between 20-30 nonfiction works cover-to-cover per year. …

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Living Values

In the open letter we wrote to the College of Arts & Letters community in January 2018, we promised to look critically at ourselves, recognize our failures, and rebuild the trust that is required of us. This commitment has led to an intense period of critical self-reflection in the Dean’s Office and across the College in …

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Of Typewriters and Permutations (II)

This continues my previous post about the problem of optimally laying out a one-dimensional typewriter keyboard, where “optimally” is taken to mean minimizing the expected amount of lateral movement to type a few selected books. As I noted there, Nate Brixius correctly characterized the problem as a quadratic assignment problem (QAP). I’ll in fact try …

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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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A Few Reflections on the TOME Initiative

WASHINGTON, DC – Today a group of colleagues from the Association of American Universities, Association of Research Libraries, and Association of University Presses met to advance the Towards an Open Monograph Ecosystem (TOME) initiative. It was heartening to see the progress the initiative has made since our first gathering in the summer of 2016. At the time, I was enthusiastic …

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Selecting Box Sizes

Someone posted an interesting question about box sizes on Mathematics Stack Exchange. He (well, his girlfriend to be precise) has a set of historical documents that need to be preserved in boxes (apparently using a separate box for each document). He wants to find a solution that minimizes the total surface area of the boxes …

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Evolution of a (data) visualization

Last summer, I taught the MAET Year 2 Summer Cohort with Danah Henriksen. After teaching the class, Danah realized she had taught five cohorts of (awesome) students and that we had some information available from pre- and post-course self-reported surveys to understand how students grew in terms of their confidence in using different educational (and …

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Callback Cuts That Repeat

The following post is specific to the CPLEX integer programming solver. I have no idea whether it applies to other solvers, or even which other solver have cut callbacks. Every so often, a user will discover that a callback routine they wrote has “rediscovered” a cut it previously generated. This can be a bit concerning …

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Grouping Rows of a Matrix

I spent a large chunk of yesterday afternoon doing something I thought would be simple (relatively speaking) in LaTeX. I wanted to group rows of a matrix (actually, in my case, a vector) with right braces, and label the groups. An example of what I wanted is in the image below. This seems to me …

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Big M and Integrality Tolerance

A change I made to an answer I posted on OR-Exchange, based on a comment from a well-informed user of OR-X, might be worth repeating here on the blog. It has to do with issues that can occur when using “big M” type integer programming models, a topic I’ve covered here before. As I mentioned …

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Cultivating a Culture of Trust

It has been difficult to write for the public in the months since posting the Open Letter to the College of Arts & Letters in the wake of the survivor impact statements that are transforming Michigan State University.1 Part of the difficulty is what my thoughtful #SpartanDean colleague, Prabu David, emphasized when he wrote that it is challenging to find the right …

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Stephen Hawking (1942-2018)

Roger Penrose writes in the Guardian, providing a scientifically precise summary of Hawking’s accomplishments as a physicist (worth reading in full at the link). Penrose and Hawking collaborated to produce important singularity theorems in general relativity in the late 1960s. Here is a nice BBC feature: A Brief History of Stephen Hawking. The photo above …

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How NSA Tracks You (Bill Binney)

Anyone who is paying attention knows that the Obama FBI/DOJ used massive government surveillance powers against the Trump team during and after the election. A FISA warrant on Carter Page (and Manafort and others?) was likely used to mine stored communications of other Trump team members. Hundreds of “mysterious” unmasking requests by Susan Rice, Samantha …

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National Indian Law Library Bulletin (2/22/2018)

Here: The National Indian Law Library added new content to the Indian Law Bulletins on 2/22/18. U.S. Supreme Court Bulletin http://www.narf.org/nill/bulletins/sct/2017-2018update.html Petition for certiorari was denied in Renteria, et al. v. Superior Court of California, Tulare County, et al. (Indian Child Welfare Act) and in Norton, et al. v. Ute Indian Tribe of the Uintah and Ouray Reservation, et …

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Documentary Films as Soccer Storytelling

I recently went on a cinematic journey that took me from women’s soccer in Zanzibar to a failed stadium-and-entertainment complex in Buenos Aires. My travel agency, so to speak, was the Football Scholars Forum. On February 23 it held an online discussion of two low-budget, high-return documentary films. (A recording of the event can be found here. …

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A Compass for the Future

Michigan State University (MSU) is making national and international news. And it’s not for its prowess on athletic fields or courts. In fact, as I’m sure everyone reading this is aware, it is for the tragedy of sexual abuse that went on for years without being stopped. The president is gone, the gymnastics coach is …

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A Transformative Moment

While I have been retired from Michigan State University for three years, I spent 30 years of my life walking the campus, teaching classes, helping students and faculty uncover information they sought, active in faculty governance and founding and directing sustainability operations. It is no small part of my life. So it is not without …

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A Shiny interactive web application to quantify how robust inferences are to potential sources of bias (sensitivity analysis)

We are happy to announce the release of an interactive web application, Konfound-It, to make it easy to quantify the conditions necessary to change an inference. For example, Konfound-It generates statements such as “XX% of the estimate would have to be due to bias to invalidate the inference” or “an omitted variable would have to …

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Outcomes from a self-generated utility value intervention in science (in IJER)

The Scientific Practices project, was focused on engaging middle school students in scientific and engineering practices (such as developing and using models, constructing explanations of phenomena, and analyzing and interpreting data). As part of this longitudinal project, we carried out field experiments to understand the impact of specific features of the curriculum. In this paper published …

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