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

introduction

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.

Happenings – 2013 Feb 2

I think I’m going to do something different this weekend… and I don’t know that it will lead to a technical post on Monday… but it seems to be what I need to do.

Play with MATLAB. We’re using it in two of the courses I’m taking – Image Processing, and Control of Mobile Robots. So I’ve got a backlog of work in the Image Processing class, and I ought to get moving in the Controls class. On top of it all, as I’ve said before, I’ve got a hefty pile of books that use MATLAB.

Now, the student version prohibits me from using it for commercial or professional purposes. I don’t care to argue with them over whether this blog is “professional”, so unless I buy my own full-fledged version, I believe that it is simpler to not publish any of my MATLAB exercises out here – not unless I move up from the student license.

So I’ve got MATLAB itself to play with, and Simulink… and toolkits for image processing, controls, and symbolic calculations, and wavelets… and more, but that’s a heck of a lot to look at already.

Unless something quick and easy pops into my head over the weekend, I expect no technical post to go out this Monday. I expect to be doing plenty of applied mathematics, I just don’t expect to publish any of it.