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# Introduction: Andrew Ardill

Hi everyone, I studied Pure and Applied Mathematics at UNSW a few years back, and currently work as a Business Intelligence Analyst.

My mother loves to tell people that during the course of asking why I wanted to study mathematics at university I said "You don't go to university to get a job" and for what it's worth I still mostly stand by that!

I enjoy spending time studying mathematics and programming, but find too often that I just read interesting things without engaging with it myself, and having read far too many interesting things about category theory decided now is the time to engage with it.

At some point I want to revisit my thesis topic, wallowing underdeveloped and unresolved in the back of my mind, on the reversibility of symbolic dynamical systems and analogues in a specific geometric space, and who knows this may be the first step.

Looking forward to learning with you all.

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edited April 2018

Glad to have you here! I've got a book by my bed called Chaos on the Interval, and it's pretty amazing, but I haven't had time to read it. It's about maps from the interval to itself. It doesn't get into "symbolic dynamical systems", but it's probably connected.

Comment Source:Glad to have you here! I've got a book by my bed called _[Chaos on the Interval](https://www.math.u-psud.fr/~ruette/articles/chaos-int.pdf)_, and it's pretty amazing, but I haven't had time to read it. It's about maps from the interval to itself. It doesn't get into "symbolic dynamical systems", but it's probably connected.
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edited April 2018

Thanks @JohnBaez #1, looks like I might have to add that to my reading list as well.

The specific thing I was looking at were two dynamic systems that we could relate together.

The first was symbolic, where a point was defined as a sequence of symbols (1s and 0s) with a marker denoting the 'current' symbol, a point. For example $$...101.001...$$

The space was defined as the set containing all such points.

The dynamics was given by a step function, that moves the marker one symbol to the right: $$...101.001... \rightarrow ...1010.01...$$

The other system was a unit square, with a step function that cuts the square horizontally into two pieces, then reshapes those pieces into a new unit square such that the top half becomes the left half, and the bottom half becomes the right half.

You can relate these two systems by following a point in the unit square as it gets moved around by the step function. If it is in the top half, say it is currently in state $$0$$, in the bottom half it is in $$1$$. After the step function it will either still be in the top half, or now in the bottom half. Following the point forwards gives you half of its symbolic analogue (everything to the right of the marker) and following it backwards gives you everything to the left.

The question I was looking into?

It's easy to reverse the symbolic system - simply flip every symbol around the marker: $$...101.001... \rightarrow ...100.101...$$

What does this look like for points in the unit square?

With the simplest step function as described above it is equivalent to flipping the square along the line $$x = y$$.

The harder part is when you realise you can define very similar step functions on the unit square which correspond to the same symbolic system, such as taking the top third to the left third and the bottom two-thirds to the right two-thirds. The simple geometric reversing flip doesn't quite work any more, and I'm not really sure why - what is the key difference between the two situations?

Comment Source:Thanks @JohnBaez #1, looks like I might have to add that to my reading list as well. The specific thing I was looking at were two dynamic systems that we could relate together. The first was symbolic, where a point was defined as a sequence of symbols (1s and 0s) with a marker denoting the 'current' symbol, a point. For example \$$...101.001...\$$ The space was defined as the set containing all such points. The dynamics was given by a step function, that moves the marker one symbol to the right: \$$...101.001... \rightarrow ...1010.01...\$$ The other system was a unit square, with a step function that cuts the square horizontally into two pieces, then reshapes those pieces into a new unit square such that the top half becomes the left half, and the bottom half becomes the right half. You can relate these two systems by following a point in the unit square as it gets moved around by the step function. If it is in the top half, say it is currently in state \$$0\$$, in the bottom half it is in \$$1\$$. After the step function it will either still be in the top half, or now in the bottom half. Following the point forwards gives you half of its symbolic analogue (everything to the right of the marker) and following it backwards gives you everything to the left. The question I was looking into? It's easy to reverse the symbolic system - simply flip every symbol around the marker: \$$...101.001... \rightarrow ...100.101...\$$ What does this look like for points in the unit square? With the simplest step function as described above it is equivalent to flipping the square along the line \$$x = y\$$. The harder part is when you realise you can define very similar step functions on the unit square which correspond to the same symbolic system, such as taking the top third to the left third and the bottom two-thirds to the right two-thirds. The simple geometric reversing flip doesn't quite work any more, and I'm not really sure why - what is the key difference between the two situations?
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Hi! I'm too sleepy to think about the math you're explaining right now. I just wanted to say:

I've added a page about you on the Azimuth Wiki, based on yours here. You can edit it as you want.

Now, if you edit an Azimuth Wiki page and sign in using the name Andrew Ardill, a link to your page will become visible on that page. We do this to make it easy for people to learn about the people who are editing this wiki.

Comment Source:Hi! I'm too sleepy to think about the math you're explaining right now. I just wanted to say: I've added a [page about you](http://www.azimuthproject.org/azimuth/show/Andrew+Ardill) on the Azimuth Wiki, based on yours here. You can edit it as you want. Now, if you edit an Azimuth Wiki page and sign in using the name Andrew Ardill, a link to [your page](http://www.azimuthproject.org/azimuth/show/Andrew+Ardill) will become visible on that page. We do this to make it easy for people to learn about the people who are editing this wiki.