Learning on traviscj/blog

todobackend.com

Fri, 05 Jan 2018 00:01:00 +0000

TodoBackend.com defines a simple API and has a frontend that works given any backend URL.

Particularly interesting to me:

haskell
- super concise!
- whoa, 6 different backends!
- spock backend is crazy concise.
python + flask
- seems like it would greatly benefit from a Store object
scala + akka
- crazy pattern matching in routes definition
java + mangooio + jOOQ
- especially the distinction between Todo and TodoPatch
- also really glad I don’t have to write routes config separately from the code!
clojure + jetty/compojure + postgresql
rails
go + goa

basic http requests and server handlers in clojure

Wed, 01 Feb 2017 00:00:00 +0000

I’ve been playing around a tiny bit with clojure, and wanted to document the process of doing something pretty basic: make a project that can request my website over HTTPs.

The first step is pretty easy:

brew install leiningen
lein new random-experimentation
cd random-experimentation

and add [clj-http "3.4.1"] to project.clj.

The HTTPS part is a bit trickier. The JDK doesn’t include the Letsencrypt certificates. But I found a simple script install-letsencrypt-in-jdk.sh that can set it up.

stocks and options from 30k feet

Fri, 14 Oct 2016 00:00:00 +0000

One of my friends at work asked me if I had any book recommendations for learning about stocks and options. Mentally, I break trading down into two general classes of trading: index-type and “exotic” trading. By exotic trading, I mean picking individual stocks/options and actively trading. This runs counter to the more conservative buy-and-hold, index-based, hands-off approach.

For the exotic trading, I learned most of what I know from a class with Professor W.E. Olmstead and his book, Options for the Beginner and Beyond: Unlock the Opportunities and Minimize the Risks. For the option-uninitiated, the basic idea is that instead of buying or selling stocks directly, you buy and sell contracts that give you the right (but not obligation) to buy or sell the stock at a particular price by a particular date. That’s a mouthful and options are indeed subtle beasts, but they allow the flexibility to either hedge risks you want less exposure to, or increase/leverage exposure to risks you do want to take.

slide rules

Wed, 19 Nov 2014 00:00:00 +0000

Suppose you want to evaluate the multiplication problem $C = A\cdot B$. But you forgot your times tables, so you are stuck using your expedition watch or something. In fact, you can even make your own out of a couple of slips of paper, if you really need to.

First bit of background: One of the rules you probably learned and I definitely forgot was the rule of logs: $$ C = A\cdot B \equiv \log C = \log(A\cdot B) = \log A + \log B$$ This ends up being useful for slide rules, because you can easily add distances together by putting two things next to eachother! So that is exactly what we do. We add the logarithms by putting things next to eachother.

black box machine learning

Tue, 15 Jul 2014 00:00:00 +0000

During my Ph.D. I studied optimization algorithms. Optimization algorithms are typically an integral part of machine learning algorithms, and we discussed many machine learning algorithms, but somehow I made it through without doing very much actual machine learning training or prediction tasks.

It turns out that it isn’t very hard to do some very basic machine learning:

pip install -U numpy scipy scikit-learn
ipython
from sklearn.ensemble import RandomForestClassifier
from sklearn import datasets
iris_data = datasets.load_iris()
rfc = RandomForestClassifier()
rfc.fit(iris_data['data'], iris_data['target'])
rfc.predict([6.1,2.6,5.6,1.4])    # yields array([2])
rfc.predict([5.7,4.4,1.5,0.4])    # yields array([0])

language fluidity

Sun, 29 Dec 2013 00:00:00 +0000

I have learned a lot of programming languages over the course of my life. So I wanted to do two things:

Discuss a few effective ways to pick up a new language.
Discuss a few references that I’ve found helpful for some languages. I should start with a disclaimer: I do enjoy learning new languages, but mostly I enjoy creating things in those languages. I’m not sure all the effort I have spent learning many languages would not have been better spent learning many fewer languages to a deeper level, but I do feel like it is extremely important to learn principles, not languages, and to use the best tool for a particular job. Many times principles are most clearly illustrated with contrast between languages, and many more times a particular tool has been a patently poor choice for a particular job.

That being said, it’s important to know your “first tongue” languages in significant depth.

a really simple iterative refinement example

Thu, 17 Oct 2013 00:00:00 +0000

I wanted to have a quick example of what iterative refinement is and looks like.

Suppose you wanted to solve the (very simple!) problem of solving 5.1x=16, without dividing by decimal numbers. (Yes, this is a bit contrived–I’m not sure why you would be able to divide by an integer to get a decimal, but not divide by a decimal to get a decimal. Bear with me.)

The standard way would be, of course, to simply evaluate x = (5.1)^{-1}16=3.137254. But this is not available–you can’t find an inverse of multiplying by 5.1!

C/C++ Values, Pointers, and References

Fri, 20 Sep 2013 00:00:00 +0000

I had an embarrassing realization: While C does have an address-of operator, it does not include reference variable or pass-by-reference syntax. It’s embarrassing because I should have realized that it was a C++ invention; I guess some of my “C” code actually really has been C++ code.

For future reference, here’s the current summary of my understanding:

	var	*var	&var
int xv=3;	value	invalid	memory location of value
int *xp=&xv;	memory location	value	memory location of pointer.
int &xr=xr;	value	invalid	memory location of value	(all invalid in C)

As one other note, there are three ways you can pass things in C:

python decorators

Tue, 30 Jul 2013 00:00:00 +0000

I came across something that I think is actually pretty neat. Python supports ``decorating’’ functions, which lets you define behaviors that essentially wrap around a given function. The benefit is that you can write a simple function and decorate it to do something fancier.

I realized I wanted to do this with a simple timing output. Say my function was just something really simple like

def f_plain(x,y):
    print("x + y = {}".format( x+y))
    return x+y
print ("---")
print (f_plain(1,3))

Now, to time it, I could define a function like:

Perturbation Theory Problems with bvp4c

Mon, 22 Oct 2012 00:00:00 +0000

I have been watching Nathan Kutz’ lectures on Coursera. One change he made to the course since I took AMATH 581 at University of Washington was introducing the MATLAB function bvp4c. I immediately realized that this would be nice for solving boundary layer problems that arise in asymptotics.

Following my life philosophy of doing the dumbest thing that could possibly work, I tried implementing Nathan’s code for a single-layer boundary layer problem from Holmes, Chapter 2:

Five Critical Textbooks for (Applied!) Math & Physics Students

Sun, 04 Sep 2011 00:00:00 +0000

In the course of working through my first year at grad school, I’ve come up with five favorites for the basics of an undergrad understanding of the essential topics for applied math and physics. Without ado and in the order I’d take them off my shelf:

Mathematical Methods in the Physical Sciences - ML Boas. This is my favorite, because it contains almost every technique you need, and it has a ton and a half of problems(over 3400). It contains a good review of complex analysis, linear algebra, differential equations, and calculus, but also chapters on special functions, partial differential equations, probability, tensors, and the calculus of variations. – Hidden Gem: Chapter 4, Section 12: Differentiation of Integrals, RP Feynman’s favorite trick.
Calculus - Greenspan. A great reference on calculus.
Complex Variables and Applications - Brown & Churchill: The most readable book on complex analysis I’ve read. Not so hidden gem: Most of the solutions are given right alongside the problem–a great book for self-study. Also the material on conformal mapping and fluid flows.
Linear Algebra And Its Applications - Strang. Nice book on linear algebra theory. – Hidden Gem: Chapter 7, Section 4: Iterative Methods for Ax=b and Gershgorin’s circle theorem.
Elementary Differential Equations and Boundary Value Problems - Boyce & DiPrima. Powerhouse of differential equation knowledge. Strangely, it is the book ESAM recommended, but not the book they use for teaching their undergrads.

I’ve spent probably the most time with Boas’ Mathematical Methods in the Physical Sciences–I’ve worked nearly 1000 problems out of the book to get ready for the preliminary exams my first year. It was completely worthwhile.

Tunes U and Essential Mathematica

Sun, 13 Dec 2009 00:00:00 +0000

In a similar vein to the TED talks in the previous post, I’ve also been watching a lot of lectures from iTunes U lately. Mostly to get ready for preliminary exams, but also for their sheer awesomeness of the teaching and material. I’ve been most surprised how many people haven’t heard of this yet: Nearly everyone seems surprised when they hear about it. Anyways, here’s my list of favorites so far:

TED Talks

Thu, 26 Nov 2009 00:00:00 +0000

I’ve been downloading a lot from iTunes recently, both in the form of TED talks and iTunes U videos. I’ll post about iTunes U later.

TED talks, for the uninitiated, are 5-20 minute lectures on something that someone(usually a researcher or philanthropist) has been working on to make the world a better or cooler place. I’ve been watching them the last few days, and they’re really great for hearing an opinion you might not, otherwise. A few of my favorites, in no particular order:

Getting an AMATH Minor at the University of Washington

Sun, 26 Oct 2008 00:00:00 +0000

One of the secret gems at the University of Washington is the minor in applied math option. At least I think it’s somewhat secret. Most of the people I tell about it haven’t really heard of it. But yeah, here’s the deal: You only need to get through calculus and four more classes to get this minor! And a lot of programs require calculus anyways. I’ve taken most of the undergrad AMATH courses, so I figured I’d write something up about which ones I recommend the most.

Odegaard Copy Center

Mon, 23 Jun 2008 12:00:00 +0000

This is going to be sortof a short post with not much worldwide applicability, but I just learned a couple of weeks ago that Odegaard’s Copy Center will bind a packet of papers for fairly cheap, it turns out. They do it with a clear front cover and a back cover of your choice, plus binding you pick out from their samples. They do it while you wait and have good hours. I had no idea they offered this service, and was very impressed with their output.

Python Playing

Fri, 28 Dec 2007 12:00:00 +0000

I’ve been playing around with Python a bit more over the break, mostly because I want to be lazy in my code-writing for the forseeable future, plus I’d like to give NumPy a shot, but I want to have a solid background before trying that. One thing that just has not gotten old yet is the ability to assign functions absolutely anywhere in python. You can pass them around like variables, put them in dictionaries, return them from functions, whatever. I mean, I lived in parenthesis for a while in my scheme class, so it’s not like I haven’t been exposed to it, but it’s still damn cool. You can do cool stuff like making a tuple of some index, some value, and the function to process the other two. That makes it so much easier to deal with various combinations of neat datastructures. Anyways, the book I’ve been reading is Dive Into Python, off diveintopython.org. I’m currently at about page 114 out of 327, and I’ve fairly faithfully read most of it up until that point. The format seems slightly frustrating to me, but it’s probably just because it’s such a departure from what a lot of books and tutorials use. It seems helpful and worthwhile in any case.