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**+** math

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.

3
Little `\pi`,

1
what

4
can you tell us?

Welcome to this year's celebration of `\pi` and mathematics. Among the chaos of CORVID-19, this year `\pi` Day celebrations are short poetic emissions I call “piku”. They are brief pauses for the time.

Start by reading how piku are constructed and then browse submitted piku. Consider participating by submitting your own piku. All you need is a pen and a few (small) words. Very therapeutic.

But if the words here don't help, immerse yourself in my coronavirus art. It's quite catching.

If you enjoy poetry and words, see how I convert spam into poems in the style of ee cummings and if you like to see words arrange on page, look through my typographic art.

Contribute by tweeting your `#piku`

creation for `#piday`

. Or email me.

3
Circles and

1
Lines

4
Unified. `\pi`!

Cath Ennis
via twitter

To fully grok the next set of piku, you need to know something about the Feynman Point.

3
Nine nine nine

1
nine

4
nine nine and so

1
on.

Paulina Rowicka
via twitter

3
Feynman point

1
at

4
seven six two.

Paulina Rowicka
via twitter

3
Feynman point

1
is

4
six nines in `\pi`.

Paulina Rowicka
via twitter

3
Next reply

1
to

4
follow quite soon.

Paulina Rowicka

3
Birds on wa-

1
-ter

4
A parking lot

1
Walk

5
on grey Step on a

9
crack; cement paw prints; immortalized

2
Break mom's

6
back grey green, yellow, red

5
green creeping up the

3
chain-link fence

5
the promise of rain

8
spots of moss abandoned mattress

9
quiet aesthetic terror; mountains

Viorica Hrincu

3
Point and click

1
click

4
click and submit

1
and

5
wheels go up, I down

9
Rollover, double tap, search engine

2
growling

6
Open tab, scroll to load

5
Click click click accept

3
Submission

5
Wait wait wait waiting

8
Trace the route in milliseconds

9
Longer waits acceptable if some

7
Not yet defined condition

9
Satisfied among these falsetruehoods

3
Piku are

1
brief

4
pauses just in

1
time.

3
Three one four

1
One

4
Five nine two six.

2
Roughly

2
the same

7
is frequently good enough.

6
Two times by anyone

2
equals

8
one time by anytwo, I hope.

3
Numbers act

1
we

4
are the audience

3
Body a

1
shell.

4
Mind a pearl with

1
in.

3
Land meets sky.

1
Oh,

4
It's you again!

1
Yes,

5
Who did you expect?

3
The sky is

1
full

4
but makes space for

1
us.

3
No no no,

1
yes.

4
You make up my

1
mind

3
Gone crazy,

1
now

4
going viral.

3
Life is long,

1
but

4
some parts are short.

3
Memories

1
for-

4
get yourself then.

3
Pain to feel,

1
more

4
than you can see.

3
Hot air breeze

1
cools

4
much hotter things.

3
F 0 0

1
red

4
You add the light.

3
All I hear

1
is

4
this corona.

3
Contact lost

1
alone

4
blurry faces

1
far

5
on the horizon.

3
Pi never

1
ends

4
unlike outbreaks.

3
Reason on

1
brain

4
kindness in heart.

3
Unknown ends

1
un-

4
known beginnings

1
start.

3
Ducks on pond

1
paired

4
except this one.

3
Words chase words

1
then

4
period like this

1
one.

A series based on `\pi`, `e`, the natural logarithm, and `\phi`, the Golden ratio.

3
This orbit

1
dance

4
no basic step.

2
Adding adding,

7
more more more still still still not

1
enough.

1
Ideal,

6
geometry, and then

1
you.

1
Dust

4
in space vacuum

0

3
clogs alien

2
machines.

0

2
Bummer.

0

news
**+** thoughts

*Huge empty areas of the universe called voids could help solve the greatest mysteries in the cosmos.*

My graphic accompanying How Analyzing Cosmic Nothing Might Explain Everything in the January 2024 issue of Scientific American depicts the entire Universe in a two-page spread — full of nothing.

The graphic uses the latest data from SDSS 12 and is an update to my Superclusters and Voids poster.

Michael Lemonick (editor) explains on the graphic:

“Regions of relatively empty space called cosmic voids are everywhere in the universe, and scientists believe studying their size, shape and spread across the cosmos could help them understand dark matter, dark energy and other big mysteries.

To use voids in this way, astronomers must map these regions in detail—a project that is just beginning.

Shown here are voids discovered by the Sloan Digital Sky Survey (SDSS), along with a selection of 16 previously named voids. Scientists expect voids to be evenly distributed throughout space—the lack of voids in some regions on the globe simply reﬂects SDSS’s sky coverage.”

Sofia Contarini, Alice Pisani, Nico Hamaus, Federico Marulli Lauro Moscardini & Marco Baldi (2023) Cosmological Constraints from the BOSS DR12 Void Size Function *Astrophysical Journal* **953**:46.

Nico Hamaus, Alice Pisani, Jin-Ah Choi, Guilhem Lavaux, Benjamin D. Wandelt & Jochen Weller (2020) Journal of Cosmology and Astroparticle Physics **2020**:023.

Sloan Digital Sky Survey Data Release 12

Alan MacRobert (Sky & Telescope), Paulina Rowicka/Martin Krzywinski (revisions & Microscopium)

Hoffleit & Warren Jr. (1991) The Bright Star Catalog, 5th Revised Edition (Preliminary Version).

*H*_{0} = 67.4 km/(Mpc·s), *Ω*_{m} = 0.315, *Ω*_{v} = 0.685. Planck collaboration Planck 2018 results. VI. Cosmological parameters (2018).

*It is the mark of an educated mind to rest satisfied with the degree of precision that the nature of the subject admits and not to seek exactness where only an approximation is possible. —Aristotle*

In regression, the predictors are (typically) assumed to have known values that are measured without error.

Practically, however, predictors are often measured with error. This has a profound (but predictable) effect on the estimates of relationships among variables – the so-called “error in variables” problem.

Error in measuring the predictors is often ignored. In this column, we discuss when ignoring this error is harmless and when it can lead to large bias that can leads us to miss important effects.

Altman, N. & Krzywinski, M. (2024) Points of significance: Error in predictor variables. *Nat. Methods* **20**.

Altman, N. & Krzywinski, M. (2015) Points of significance: Simple linear regression. *Nat. Methods* **12**:999–1000.

Lever, J., Krzywinski, M. & Altman, N. (2016) Points of significance: Logistic regression. *Nat. Methods* **13**:541–542 (2016).

Das, K., Krzywinski, M. & Altman, N. (2019) Points of significance: Quantile regression. *Nat. Methods* **16**:451–452.

*Nature uses only the longest threads to weave her patterns, so that each small piece of her fabric reveals the organization of the entire tapestry. – Richard Feynman*

Following up on our Neural network primer column, this month we explore a different kind of network architecture: a convolutional network.

The convolutional network replaces the hidden layer of a fully connected network (FCN) with one or more filters (a kind of neuron that looks at the input within a narrow window).

Even through convolutional networks have far fewer neurons that an FCN, they can perform substantially better for certain kinds of problems, such as sequence motif detection.

Derry, A., Krzywinski, M & Altman, N. (2023) Points of significance: Convolutional neural networks. *Nature Methods* **20**:1269–1270.

Derry, A., Krzywinski, M. & Altman, N. (2023) Points of significance: Neural network primer. Nature Methods **20**:165–167.

Lever, J., Krzywinski, M. & Altman, N. (2016) Points of significance: Logistic regression. Nature Methods **13**:541–542.

*Nature is often hidden, sometimes overcome, seldom extinguished. —Francis Bacon*

In the first of a series of columns about neural networks, we introduce them with an intuitive approach that draws from our discussion about logistic regression.

Simple neural networks are just a chain of linear regressions. And, although neural network models can get very complicated, their essence can be understood in terms of relatively basic principles.

We show how neural network components (neurons) can be arranged in the network and discuss the ideas of hidden layers. Using a simple data set we show how even a 3-neuron neural network can already model relatively complicated data patterns.

Derry, A., Krzywinski, M & Altman, N. (2023) Points of significance: Neural network primer. *Nature Methods* **20**:165–167.

Lever, J., Krzywinski, M. & Altman, N. (2016) Points of significance: Logistic regression. Nature Methods **13**:541–542.

Our cover on the 11 January 2023 Cell Genomics issue depicts the process of determining the parent-of-origin using differential methylation of alleles at imprinted regions (iDMRs) is imagined as a circuit.

Designed in collaboration with with Carlos Urzua.

Akbari, V. *et al.* Parent-of-origin detection and chromosome-scale haplotyping using long-read DNA methylation sequencing and Strand-seq (2023) Cell Genomics 3(1).

Browse my gallery of cover designs.

My cover design on the 6 January 2023 Science Advances issue depicts DNA sequencing read translation in high-dimensional space. The image showss 672 bases of sequencing barcodes generated by three different single-cell RNA sequencing platforms were encoded as oriented triangles on the faces of three 7-dimensional cubes.

More details about the design.

Kijima, Y. *et al.* A universal sequencing read interpreter (2023) *Science Advances* **9**.

Browse my gallery of cover designs.

Martin Krzywinski | contact | Canada's Michael Smith Genome Sciences Centre ⊂ BC Cancer Research Center ⊂ BC Cancer ⊂ PHSA

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