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Mark Davis

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By Presidential decree, January 20th, 2017 has been named "National Day of Patriotic Devotion."

I shit you not. It is in the Federal Register, right here:

Our new government's propaganda department apparently has very twentieth-century tastes. I'm mentally interpreting this as an attempt to say "Все-страны день преданности Родине" in English, possibly by a fluent but non-native speaker.

h/t to @kenklippenstein over at Twitter for spotting this.

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Triple Pendulum Control

A few years ago Dr. Tobias Glück from Technische Universität Wien, found that along with his mathematical insights, computers and numerical methods were now fast enough to swing-up and balance a pendulum, on a pendulum, on pendulum on a sliding rail under computer control.

IEEE CSS Video Clip Contest 2014 Submission

Triple Pendulum on a Cart (YT ~1 min.):

The presented work deals with the swing-up of the triple pendulum on a cart. The swing-up maneuver is accomplished within a two-degrees-of-freedom control scheme consisting of a nonlinear feedforward controller and an optimal feedback controller. Based on a precise mathematical model, the feedforward controller was obtained by solving a nonlinear two-point boundary value problem with free parameters. A time-variant Riccati Controller was developed in order to stabilize the system along the nominal trajectory and an Extended Kalman Filter was used to estimate the non-measurable states. The overall control strategy for the swing-up maneuver was successfully implemented and tested on an experimental test bench. Up to the authors’ knowledge, this is the first contribution so far providing numerical and experimental results of the swing-up maneuver for a triple pendulum on a cart.

Paper (open pdf):

Tobias Glück:

Here is an easy to follow and graphic explanation of Kalman filters due to Tim Babb, who lives in the San Francisco Bay Area, and is Lighting Optimization Lead for Pixar Animation Studios.

Related Post:

Animated Photo

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The news about Nazis in DC may have hidden some of the most important stories brewing about the new administration. This one may prove to have some of the most serious consequences. Trump wants to eliminate NASA's Earth Science division, one of the foremost institutions in the world studying the state of our planet. This team has key responsibilities in lofting the satellites which give us a view of what's happening around us – as well as being one of the world's best groups of climate modeling.

Eliminating the division would both disband one of the best such teams in the world, and eliminate nearly $2B of funding from the subject, costing hundreds (or more) of jobs across the field, and likely most affecting the careers of young researchers – with huge consequences for the field's future, just as it is becoming ever-more critical. (Remember that the Arab Spring was triggered by droughts in Asia and the Middle East, and the current massive surge in temperatures in the Arctic – it's currently 36°F above normal! – are going to have tremendous consequences. There's a reason the DoD considers this a top strategic priority.)

More chillingly still, the justification for this is that he calls their work "politicized science" – which is to say, "science which is politically inconvenient for him." We've seen a similar game in which Congress has banned any medical or epidemiological research on guns, because of the NRA's (probably justified) fear that the results of even the most trivial research would harm their political goals.* (Pro tip: if you know that anyone seriously looking at a question will come up with answers that hurt your goals, this may mean your goals are shady.)

There's actually a name for this sort of thing: Lysenkoism, named after Soviet agriculture director Trofim Lysenko. Lysenko considered genetics to be politically unfavorable to Communism, because if traits are inherent, then they can't be improved by the government, and that would make all sorts of parts of the Five-Year Plan obviously infeasible. With Stalin's enthusiastic support, all funding for research which disagreed with this was cut. (And this being Stalin, researchers who disagreed were shipped to Siberia) It was replaced by a rather bizarre official theory in which, for example, rye could be turned into wheat, and exposing wheat seeds to high humidity and low temperature would "teach" them and their descendants to grow in the winter.

The thing about science is that it's about asking questions and noting what's happening in the world around you. You don't get to make theories up and just say that the world is so; all you can do is describe what's actually observed, and try to figure out if you can predict what will happen next. That is, science is descriptive, it's not normative.

And that means that science is about things that keep happening, whether you believe in them or not. Unlike saying "I don't believe in fairies!," you can say "this wheat will grow in Siberia!" as often as you like, and the wheat still isn't going to grow there. That's the problem with Lysenkoism: it's based on pretending that nature works some way, and threatening anyone who dares to disagree with you, but nature doesn't really care. It will keep doing what it was doing before, and all that happens is that you've decided to be officially blind to it.

You do this with how crops work, and you end up with unexpected famines. You do this with how climate works, and you end up with unexpected droughts, floods, spreads of new diseases, and all sorts of fun and exciting things, because it turns out that the weather is still pretty important in our lives and you do not fuck with the laws of physics.

I say this with confidence: I was a physicist myself, am currently an engineer, and so if anyone is qualified to make a snappy answer to "Ye cannae the laws of physics, Jim!" it's probably me. But sorry: if your politics would be harmed by people being aware of reality, then all that means is that (a) your politics are apparently based on lying to people, and (b) at some point or another you are going to get a rude introduction to reality, which will not be good for either your politics or your constituents-slash-victims.

* Before anyone uses this as an excuse to go on a rant: I'm not anti-gun at all, and rather enjoy shooting. But there's a huge space between the Second Amendment and the sort of lunacy that the NRA has gotten infatuated with, where any restriction on a person's right to own a GBU-31 JDAM is tantamount to treason. And things like legally barring doctors from asking people if they have a gun in the house – even though, for example, that's a serious risk factor of death if anyone in the house is suffering from serious depression or similar illnesses – is just sacrificing human lives on the altar of their own political expediency. Seriously, fuck those guys.

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Don't waste your time on petitions to "Abolish the Electoral College"...this is how you can actually help ensure future Presidents are elected by popular vote:

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