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Distractions and amusements, with a sandwich and coffee.

In your hiding, you're alone. Kept your treasures with my bones.
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On March 14th celebrate `\pi` Day. Hug `\pi`—find a way to do it.

For those who favour `\tau=2\pi` will have to postpone celebrations until July 26th. That's what you get for thinking that `\pi` is wrong. I sympathize with this position and have `\tau` day art too!

If you're not into details, you may opt to party on July 22nd, which is `\pi` approximation day (`\pi` ≈ 22/7). It's 20% more accurate that the official `\pi` day!

Finally, if you believe that `\pi = 3`, you should read why `\pi` is not equal to 3.

2013 was the first year in which I made `\pi` day art. It was a year of dots and love.

René Hansen has created an interactive version of this year's posters! Why not go to the Feynman point directly!

All the posters are also available without the "`\pi` day 3 · 14" inscription.

`\pi_i` / grey 80% opacity

`\pi_i`/`\pi_{i+1}` 80% opacity

`\pi_i` / grey 80% opacity (equal neighbours connected)

`\pi_i` / `\pi_{i+1}` 80% opacity (equal neighbours connected)

— / `\pi_{i+1}` (equal neighbours connected, unconnected digits not shown)

`\pi_i` / `\pi_{i+1}` (equal neighbours connected with line width proportional to difference in neighbour digits `d in \{0,1,2\}`, unconnected digits not shown)

`\pi_i` / `\pi_{i+1}` (equal neighbours connected with line width proportional to difference in neighbour digits `d in \{0...5\}`, unconnected digits not shown)

`\pi` : — / red (equal neighbours connected, unconnected digits not shown)

`\phi` : — / white (equal neighbours connected, unconnected digits not shown)

`e` : — / grey (equal neighbours connected, unconnected digits not shown)

`\pi_i` / grey 80% opacity (equal neighbours connected)

`\pi_i` / `\pi_{i+1}` 80% opacity (equal neighbours connected)

`\pi_i` / grey 80% opacity (equal neighbours connected, unconnected digits not shown)

`\pi_i` / `\pi_{i+1}` 80% opacity (equal neighbours connected, unconnected digits not shown)

*Science. Timeliness. Respect.*

Read about the design of the clothing, music, drinks and art for the Genome Sciences Center 20th Anniversary Celebration, held on 15 November 2019.

As part of the celebration and with the help of our engineering team, we framed 48 flow cells from the lab.

Each flow cell was accompanied by an interpretive plaque explaining the technology behind the flow cell and the sample information and sequence content.

*The scientific process works because all its output is empirically constrained.*

My chapter from The Aesthetics of Scientific Data Representation, More than Pretty Pictures, in which I discuss the principles of data visualization and connect them to the concept of "quality" introduced by Robert Pirsig in Zen and the Art of Motorcycle Maintenance.

Discover Cantor's transfinite numbers through my music video for the Aleph 2 track of Max Cooper's Yearning for the Infinite (album page, event page).

I discuss the math behind the video and the system I built to create the video.

*Everything we see hides another thing, we always want to see what is hidden by what we see.
—Rene Magritte*

A Hidden Markov Model extends a Markov chain to have hidden states. Hidden states are used to model aspects of the system that cannot be directly observed and themselves form a Markov chain and each state may emit one or more observed values.

Hidden states in HMMs do not have to have meaning—they can be used to account for measurement errors, compress multi-modal observational data, or to detect unobservable events.

In this column, we extend the cell growth model from our Markov Chain column to include two hidden states: normal and sedentary.

We show how to calculate forward probabilities that can predict the most likely path through the HMM given an observed sequence.

Grewal, J., Krzywinski, M. & Altman, N. (2019) Points of significance: Hidden Markov Models. *Nature Methods* **16**:795–796.

Altman, N. & Krzywinski, M. (2019) Points of significance: Markov Chains. *Nature Methods* **16**:663–664.

My cover design for Hola Mundo by Hannah Fry. Published by Blackie Books.

Curious how the design was created? Read the full details.

*You can look back there to explain things,
but the explanation disappears.
You'll never find it there.
Things are not explained by the past.
They're explained by what happens now.
—Alan Watts*

A Markov chain is a probabilistic model that is used to model how a system changes over time as a series of transitions between states. Each transition is assigned a probability that defines the chance of the system changing from one state to another.

Together with the states, these transitions probabilities define a stochastic model with the Markov property: transition probabilities only depend on the current state—the future is independent of the past if the present is known.

Once the transition probabilities are defined in matrix form, it is easy to predict the distribution of future states of the system. We cover concepts of aperiodicity, irreducibility, limiting and stationary distributions and absorption.

This column is the first part of a series and pairs particularly well with Alan Watts and Blond:ish.

Grewal, J., Krzywinski, M. & Altman, N. (2019) Points of significance: Markov Chains. *Nature Methods* **16**:663–664.