Work – what I do to pay the bills – was quite a bit more hectic this week than usual. I was pretty tired at the end of every day.

(Don’t misunderstand, I like what I do for work, but it’s not the same as doing whatever math turns me on. No, I’m not an actor working as a waiter, or a writer working working as a housepainter. Most of my work is to model the performance of power plants, so I do get paid to do mathematical modeling. And I know how fortunate I am to do work that I love. But it’s not always the same as doing what I want.)

Interestingly, the main effect of being unable to do any math of my own during this past week is that I really want to dive into math today… but I mean math, not the writing up of math for a post!

Realistically, I’m hoping that I will either end up writing a post about something because I need a break from math per se, or that I will get the material I need for a post out of the math I do.

Today I want to tackle control theory. As usual, I won’t be doing a whole lot of theory as such. My personal ultimate goal is to get comfortable simulating control problems, and that means dealing with multiple variables, nonlinear models, and limited control responses, on top of the standard linear modeling. (For the record, i do not do controls for work. At this, I am an amateur.)

But I’ll settle for deciding upon and getting comfortable with a collection of standard graphical outputs. I’ll start by applying them to introductory problems, and complicate things as I learn more.

Oh, just about the only thing quantitative that I saw of interest this week was a newscast that starting today Californians would be required to pay sales tax on their Amazon purchases over the internet – oops, that’s not true: sales tax is unconstitutional, because it’s a tax on the produce of another state, but use tax is OK, because it’s a tax on my using the product. What we pay is a use tax numerically equal to the sales tax we pay on in-state purchases.

Bullshit. And I’m not primarily speaking of their circumventing the constitution, but of the statement that the requirement begins today. The news said that Amazon would begin collecting the tax today.

But we’ve been required to pay taxes on internet purchases for several years. There’s a line on the California income tax form just for that purpose. Of course, so few people pay it that the state can’t cope with it when I do. Two years ago they refunded it to me once, and so far this year they’ve refunded it to me twice!

Alright, enough of that. Let me pretend I’m Harry Potter at Hogwarts – only the magic I’m about to study is the mathematics of controls.

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