Happenings – 2013 Apr 13

I haven’t quite decided if Something is going on, and I haven’t decided what to do about it – oh, actually of course I have – but in the meantime, I’m going to be quiet about it. The significant alternation in my pattern is that I’m sleeping just about 8 hours every night… and I’m not taking any medication… but what is going on?

I’ll tell you more. But later.

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Happenings – 2013 Mar 30

I hate to say it, but I’m really pretty comfortable doing one course right now. The blog will just have to wait.

Oh, I did get a certificate with distinction for the controls course… I’m a little surprised, since 86% didn’t seem all that high to me… but I guess the top 10% of the scores were not 100%. Anyway, I’m still in the same condition I’ve been in for the past couple of weeks: math for the blog just doesn’t cut it right now. But who knows? The weekend is young… and we’ll see what happens.

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Happenings – 2013 Mar 23

So what’s been happening?

I’m down to one course – but I should have noticed that a quiz was due at 4 am this morning. Oh, well. We’ll see what happens.

So, I got a certificate with distinction for the image processing – but I’d really like to do some actual image processing! Didn’t actually find time to do that.

I expect to get a certificate in control of mobile robots, but the grading doesn’t actually end until midnight or something Sunday, so we’ll see. And, just as with image processing, I really need to do some controls.

There is no certificate, or even a record of my grade, for the computational finance – but that’s OK: I learned something, and that suffices. I am a little shocked that there is no record of my grade… but that’s no big deal.

So: I should start working on a technical post for Monday evening.

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Happenings – 2013 Mar 16

Okay. I’m down to one course; three of the four are finished. And I’m thinking about dropping the last one. Digital Signal Processing is an order of magnitude harder than any other MOOC (Massive Online Open Course) I’ve taken. Still, I ought to at least see where it all goes, and then drop it at the end.

I’m not working very hard at getting my tax stuff to my tax man, and I really need to get my act together on that, too. OTOH, “Warhorse” was a good movie to watch last night.

Back to the courses…. The image processing was a spectacular overview, and I really ought to do some coding for it – I have what looks like the perfect book The controls course was a marvelous insight into real control theory: we got a quick intro to PID and state space, and then focused on switching between different control strategies (go-to-goal, obstacle-avoidance, and follow-wall). I was impressed by how much controlling they did with so little theoretical machinery. I haven’t decided what I’ll do to follow up on all that. Maybe I’ll just keep on with what I (was) doing.

We’ll see whether I actually get a technical post done for this Monday….

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Happenings – 2013 Mar 9

School continues, online of course.

I have finished a second course, Image and video processing…. As usual, I’ve done what I had to, not all that I wanted to. Anyway, I’m down to two active classes. (Never again will I try 4 at once. And I’m not even thinking about the next course I’ll start yet.)

This leaves Control of Mobile Robots – where the major challenge is that we can only take each quiz twice, but I was doing OK… and Digital Signal Processing, where I have fallen quite a bit behind. For the controls course, my next quiz is due next Sunday evening. For the signals course, on the other hand, quiz 3 is due before I go to bed tomorrow. OTOH, I can take each quiz 100 times.

And this is the weekend I really ought to get all my tax stuff together for my tax man.

As for the rest of the world, I’ve noticed that physicists are not ready to declare that they have found the Higgs particle… the Pittsburgh Steelers have released James Harrison.

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Happenings – 2013 Mar 2

School continues. Online, of course… MOOCs (Massive Open Online Courses), but I’ve finished the Intro to Computational Finance. Now I have to get caught up in Digital Signal Processing and in Control of Mobile Robots. I am up-to-date in Image Processing, but we’ve just started a set of lectures on compressed sensing. I would really like to see a couple more simple examples.

In the meantime, the blog remains inactive: I’ve got too much coursework to do. This is where my major weakness comes to the fore: I sweat blood to get new computations to come out right. I have to hammer out the details before I get things. So let me dig out my hammers (Mathematica and MATLAB) and get pounding.

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Happenings – 2013 Feb 22

I dove straight into homework this morning… but let me take a break and put out my usual (and recently very short) diary post for the week.

In principle, I’m up-to-date in two of my four online courses (Image Processing, and Control of Mobile Robots). I’m not doing anywhere near what I’d like to, but I am doing what I must do.

The third course (Intro Computational Finance) is beginning to look manageable, since I’ve done most but not all of the final homework assignment. The material from week 8 took me a while to make sense of. The last homework and the final exam are due a week from tomorrow, the evening of Mar 3. This class began back in December and is just about over.

The fourth course (Digital Signal Processing) still looks wonderful, but I’ve got a pile of work due Tuesday evening. Well, with the third course looking under control, maybe I’ll get through that pile of work. Let’s see: I have to get MATLAB to draw some pictures… play another set of lectures… do some homework… and take two quizzes.

If you think there’s a technical post coming out this Monday… sorry, but I really doubt it.

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Happenings – 2013 Feb 15

Well…. All week long I had expected to say that the close approach of an asteroid was a non-event… I expected to say that it shot thru our ring of communication satellites without hitting anything, and just kept going.

And do it did. (Hmm. Would the NSA actually tell us if it lost a secret satellite?)

What none of us were expecting, of course, was the meteorite that crashed into Russia. Since it came from an entirely different direction, we believe that it was not associated with the asteroid. It broke a lot of glass, and injured a lot of people, but it wasn’t exactly devastating. I understand that people are already selling alleged pieces of it.

I’m really beginning to feel overwhelmed by my classes. I doubt that a technical post will go out this Monday, but we’ll see. At the moment, however, I don’t plan on trying to assemble one.

Control Theory: Example 3 – P-only control and offset


I want to see exactly how we get offset under P-only control, and how PI control eliminates the offset. I’m going to use Example 3 again… I’m going to look at P and PI control… and I’m going to use the Tyreus-Luyben (“T-L”) tuning rules, which we’ve seen before.

When I started this, I was wondering about two things:

  • Is the control effort nonzero when we have offset?
  • We don’t always have offset under P-only control, do we?

I can’t say I’ve become an expert in offset, but I’m a little more comfortable with it. Now what I’d like to know is why the control effort goes to zero when we do not have offset – but that’s a question still looking for an answer.

Let me tell you up front what we will find:

  • With P-only control, we may have offset: the output will not tend to the set point.
  • In that case, the use of PI-control will eliminate offset.
  • But if our plant (G) has a pole of any order at the origin, then P-only control does not lead to offset.
  • In that case, you could imagine that the plant itself includes integral control.

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Happenings – 2013 Feb 9

There have been no major changes in the past week.

Oh, I did have to report for jury duty twice in the past week. The first day, I filled out a 15-page questionnaire… the second day, having read my answers, they dismissed me from further consideration.

In the meantime, I have made a little progress on MATLAB, but I still have a lot to learn. Sometimes I feel completely overwhelmed by 3 courses and MATLAB and a blog and work – and I vow not to start the fourth class… but the actual requirements for the courses aren’t very demanding, so I’m keeping up, although I’m not doing anywhere near what I had hoped to do.

An oft-repeated question in the discussion fora for the “Control of Mobile Robots” class is: how can we have offset under proportional-only control? I think it would be worthwhile to look at that, so I expect to have a short technical post ready for this coming Monday.