
Street-Fighting Mathematics - memexy
https://mitpress.mit.edu/books/street-fighting-mathematics
======
stiff
For the people who did not notice, in the "Open Access" tab you can download
the PDF of the whole book legally and for free.

There is also a second book by the same author which is a bit harder and more
comprehensive, and also open access:

[https://mitpress.mit.edu/books/art-insight-science-and-
engin...](https://mitpress.mit.edu/books/art-insight-science-and-engineering)

~~~
sfsylvester
Also available as part of the MIT OCW[0]

[0] [https://ocw.mit.edu/courses/mathematics/18-098-street-
fighti...](https://ocw.mit.edu/courses/mathematics/18-098-street-fighting-
mathematics-january-iap-2008/readings/)

~~~
evanb
I took this course during a January term. It was great fun and Sanjoy was a
great teacher, with tons of energy and enthusiasm.

------
seven4
_" Mahajan describes six tools: dimensional analysis, easy cases, lumping,
picture proofs, successive approximation, and reasoning by analogy.
Illustrating each tool with numerous examples, he carefully separates the
tool—the general principle—from the particular application so that the reader
can most easily grasp the tool itself to use on problems of particular
interest. Street-Fighting Mathematics grew out of a short course taught by the
author at MIT"_

That short course looks like its still available on edx - though it's archived
- I seem to be able to access the material.

[https://www.edx.org/course/street-fighting-
math](https://www.edx.org/course/street-fighting-math)

~~~
mikorym
The content looks quite interesting for a mathematician too—so I'm sorry that
the advertising needs to be antagonising.

But even _Keep the Aspidistra Flying_ was basically mutilated by circumstance
[1] and it's still a great book. So, I'll take the insults towards
mathematicians with humour and actually read some of it—I often switch between
grumpy rigour to applicative speed. We all need to earn an income.

[1]
[https://en.wikipedia.org/wiki/Keep_the_Aspidistra_Flying#Lit...](https://en.wikipedia.org/wiki/Keep_the_Aspidistra_Flying#Literary_significance_and_criticism)

Edit: Just to be clear, my comment on mathematicians is not on your quote, but
this quote from OP's post:

> an antidote to mathematical rigor mortis

~~~
steev
How on earth is any of the advertising antagonizing? I had to read through the
course page twice to look for anything remotely resembling a criticism and
came up blank.

If it is the quote you added to the bottom of your comment, my question still
stands. That isn't an insult to anyone (certainly not mathematicians) but
rather a comment that many people freeze up when it comes to mathematics (at
least that was my interpretation).

~~~
mikorym
There is a somewhat common attitude towards abstract mathematics that its
preciseness is something of a bother to people and that it requires some kind
of "cure".

Immanuel Kant wrote about it [1] and many engineers have a varying degree of
animosity towards pure mathematics. So, in the book's description they say
this:

 _This engaging book is an antidote to the rigor mortis brought on by too much
mathematical rigor, teaching us how to guess answers without needing a proof
or an exact calculation._

I don't like the advertising, or the description if you will, as it basically
tries to discount rigour. One can simply say it's an _addition_ to the usual
rigour of mathematics for the sake of daily street fighting style problem
solving. The way they state it, however, it sounds like they are saying that
rigorous math is not necessary.

My reference to George Orwell is simply that when he wrote _Keep the
Aspidistra Flying_ his publishers made him write a lot of things he didn't
want to write, and they even specified the amount of words the books needed to
have (which is is somewhat understandable, but limiting still).

[1]
[https://en.wikipedia.org/wiki/Critique_of_Pure_Reason](https://en.wikipedia.org/wiki/Critique_of_Pure_Reason).
However, note that this is about _metaphysics_ and one can argue that pure
mathematics is not what he was critisising and that his work doesn't directly
try to disprove the use of axioms, without which mathematics cannot exist.

------
dls2016
I discovered Prof Mahajan through his "Teaching College-Level Science and
Engineering" course on MIT OCW. I must have watched it six times during
graduate school. He also has an OCW course based on this book.

[http://web.mit.edu/sanjoy/www/](http://web.mit.edu/sanjoy/www/)

------
hardmath123
Stanford has an excellent physics course, "Back-of-the-Envelope Physics,"
based on Mahajan's work. On the first day we worked out how much to feed a
baby every day assuming they are spherical heat emitters of radius 1 meter...
(also, you got points off the problem sets if your answers were _too_
precise).

~~~
baggy_trough
That's a big baby.

~~~
saeranv
Calculations are so much easier when it's a unit circle/sphere.

Here's my favorite trick: the radians of an angle in a unit circle is equal to
the length of the arc of that unit circle.

~~~
baggy_trough
That's not exactly a trick. It's the point of the definition.

~~~
saeranv
I think you're being needlessly pedantic. Just because it's easy to derive
doesn't mean it's immediately obvious. I only realized it when I watched a
3Brown1Blue video where he pointed it out as interesting property of the unit
circle. That alone tells me its not that obvious to many.

~~~
srean
You did not get parents comment. Its not a derivation its a definition.

~~~
saeranv
Personally, that again sounds like a very pedantic and obvious point to me.
However, I could be wrong so feel free to break down your point further.

My interpretation is that I think you guys are missing the fact that the
intent of my original comment is in the context approximations, from which you
can see the use of the 'trick' is correct.

To break it down a little further: the trick I am referring to is in practice
it's often convenient to scale approximations so that you can use the unit
circle for calculations, since you can use the radians as a measurement of arc
length. If it's not a unit circle, the angle != arc length, so that
convenience is lost.

~~~
srean
> Just because it's _easy to derive_ doesn't mean it's immediately obvious

is what I was responding to. My point is this -- there is _no_ derivation
happening there. If it was pedantic, obvious and simple to you as you claim, I
wonder why you claimed that it was a derivation.

To you the distinction between a definition and a derivation might be a
_pedantic_ one, I have doubts on whether that is an universal or even an
useful position to have.

------
nchelluri
I have a copy of this book and haven't read it. I keep fearing my background
won't be strong enough. I struggle with some high school math (I did get a
math degree many years ago but haven't kept up with even basic algebra, and it
shows). This book's preface says it complements How to Solve It, another book
I've been scared to crack open.

Nonetheless the thinness of the book and the foreword about applications and
real world math are very promising. Maybe I should try it out. Any thoughts
from someone who has read it?

~~~
blp
It is great and the math is easy. There are a couple clever tricks ( like how
to calculate pi), but nothing beyond high school math.

~~~
nchelluri
thanks :)

------
rpmuller
Sanjoy's graduate thesis covers some of the same material, and is also good
reading:

[https://thesis.library.caltech.edu/5338/](https://thesis.library.caltech.edu/5338/)

------
melvinroest
I feel that _to some extent_ this should be similar to estimation questions
that consultants face in their interviews. Questions like:

\- How many gas stations are there in Paris?

\- How much savings does the leading bank of the USA have?

\- Estimate the population of Indonesia (to someone who is not that familiar
with Asia).

It's probably a great deal more complicated than these type of questions. But
if there is a course like this and a student still feels as overwhelmed by
these type of questions, then I feel the title should be updated accordingly.

The reason I'm also mentioning this is because I'm curious if anyone did both
and can attest to whether one does get better at estimation questions like the
one I outlined. If so, I just might want to take this course, as I'd like a
deeper exploration on the topic than just consultant interview estimation
questions.

~~~
estomagordo
fwiw the types of questions you mention are often refered to as Fermi
problems, after the famous physicist.

[https://en.wikipedia.org/wiki/Fermi_problem](https://en.wikipedia.org/wiki/Fermi_problem)

~~~
melvinroest
Awesome! I'll take a look at that.

FWIW: it was worth quite a bit :)

------
slyu
I took Sanjoy's Bayesian inference course at Olin College of Engineering. One
of the few courses during my undergrad experience that just gave me pure joy
and excitement. He's one of those people who can explain seemingly complex
concepts to a 6 years old.

------
tadhgpearson
This is an awesome book - its techniques have served me well in the years
since reading it. Its small size and high information density make it a good
carry-on for flights and long bus or train journeys.

------
seesawtron
On a side note, does anyone know why certain books are restricted for sale
only in certain subcontinents? For example this book is "Not for sale on the
Indian subcontinent."

~~~
jamesmaniscalco
As far as I can tell, textbook publishers practice price discrimination so
that they can sell less expensive versions of the same book in markets where
profit is maximized at a different price. Retailers are only permitted to sell
the appropriate version in the appropriate market.

Personally I have seen many textbooks available in the US/Canada version and
Indian Subcontinent version (generally the same text, often for sale at <25%
the price). My guess is that it's common to see India in particular because
there is a large market for English-language textbooks there.

~~~
seesawtron
It falls along the same line of argument that big Journal Publishing groups
like Elsevier and Springer do the same when giving subscriptions to countries
across Europe vs Africa. I heard this in a talk from a former director of
Radboud University in Netherlands who is now spearheading the Open Science
movement in Europe.

------
archi42
Ha, I misread the title as "Street-Fighting Mathematicians" and expected
something about characters such as Galois
([https://en.wikipedia.org/wiki/%C3%89variste_Galois](https://en.wikipedia.org/wiki/%C3%89variste_Galois))

~~~
SuoDuanDao
I was expecting a hard data approach to a style of unarmed combat. Wouldn't
even be the first time something like that's been written:
[https://www.amazon.ca/dp/1904658849?tag=duc12-20&linkCode=og...](https://www.amazon.ca/dp/1904658849?tag=duc12-20&linkCode=ogi&th=1&psc=1)

------
knzhou
A beautiful book. I have all my students read it and I use its ideas every day
in research.

------
smlckz
>> Not for sale on the Indian subcontinent.

huh?

~~~
noelwelsh
I don't know if it is the case for this book, but many text books have vastly
cheaper versions that are printed in India. Usually they are on much thinner
paper. (I saw these during postgrad when some of the international students
would bring texts from their home country.)

~~~
terminalcommand
Could they have been pirating the books? In my home country (Turkey), there
were alternative sellers (basically photocopiers) who made pirate copies of
books (usually on much thinner paper and washed out colors) and sold them.
They were exactly like bookstores and they'd have the books you needed in
stock. They usually sold textbooks for 1/10th of the price.

~~~
iambrj
Pretty sure it wasn't piracy. For instance see this[0] book (not affiliated),
at the bottom left it says "Restricted! For sale only in India, Bangladesh,
Nepal, Pakistan, Sri Lanka & Bhutan"

[0] [https://www.amazon.in/Abstract-Algebra-3ed-David-
Dummit/dp/8...](https://www.amazon.in/Abstract-Algebra-3ed-David-
Dummit/dp/8126532289/ref=sr_1_7?dchild=1&keywords=abstract+algebra&qid=1593094249&sr=8-7)

------
99_00
"Mahajan describes six tools: dimensional analysis, easy cases, lumping,
picture proofs, successive approximation, and reasoning by analogy."

Reasoning by analogy sounds dodgy to me.

~~~
dls2016
Dodgy how?

I've always found that it's difficult to get a student to even venture a guess
about the answer to a problem. If they do make a guess then they probably have
a mental model about how the situation should work... and then teaching
becomes easy: either their model is good or it needs tweaking.

You gotta have the confidence to be wrong.

~~~
99_00
Using analogy to teach people something new makes sense and it's done all the
time with positive effect.

But using an analogy to infer something that hasn't been observed? Unless the
analogy is very close to the subject, it doesn't make much sense to me.

------
jansan
I was actually expecting a book that explains real street fighting with
mathematics (like kinetics of certain moves, optimizing impact on the
opponent, etc.). I am a bit disappointed after reading the abstract...

~~~
codemonkey-zeta
I've learned from acquaintances who grew up in "tough" places, where street
fights are more common, that violence is more about social posturing than it
is about the actual fighting. In these places one's reputation can be
protection. If everyone knows Bob will escalate situations to a physical
fight, then few people will confront Bob. I've heard it's analogous to
mutually assured destruction, where the "crazier", more inclined toward
violence an individual is, the less likely it is they will end up in street
fights.

I imagine if you wanted to study fighting in a mathematical way, you would
want to study experts. MMA fighters, boxers, Muay Thai fighters all optimize
their bodies and technique toward effective fighting. I bet there would be
interesting science/math there, but I doubt street fighting would actually
yield much insight.

~~~
082349872349872
Rory Miller calls the most common social posturing "the Monkey Dance."

[http://chirontraining.blogspot.com/2013/03/cofv8-monkey-
danc...](http://chirontraining.blogspot.com/2013/03/cofv8-monkey-dance.html)

related discussion:
[https://news.ycombinator.com/item?id=23429390](https://news.ycombinator.com/item?id=23429390)

(to reply directly: leverage is useful, mixed game strategies are useful,
beyond that I can't think of other applicable theories. Miller points out that
non-posturing violence is usually as unfair as possible, so maybe big-O
notation?)

