Notes on traviscj/blog

jquery selectors

Wed, 17 Oct 2018 03:51:27 +0000

This is silly, but I always forget this:

I also learned you can specify things like

// @require https://code.jquery.com/jquery-2.1.4.min.js

in a Tampermonkey script, even when a given site doesn’t already have jquery.

regex in java

Fri, 23 Feb 2018 13:41:22 +0000

I can never remember how to do java regexes with Pattern.

Pattern pattern = Pattern.compile("x_(yy|zz)");
String input = "x_yy";
boolean m = pattern.asPredicate().test(input);
System.out.println("matches: " + m);
Matcher matcher = pattern.matcher(input);
while (matcher.find()) {
  System.out.println("whole matched string: " + matcher.group(0));
  System.out.println("matched group: " + matcher.group(1));
}

I also learned a really cool thing IntelliJ can do with pattern matches!

![java regex]({{ site.baseurl }}/assets/java-regex.png)

_useful

Mon, 03 Apr 2017 00:00:00 +0000

I often create a directory/file called _useful/_useful.org/_useful.txt. I have one in my Dropbox, for example, that contains:

My apartment lease
My car/motorcycle insurance details
A textfile with my vehicle plate numbers/VINs/insurance policy numbers.

At work, I have one with

the top visited links for logs/metrics/admin interfaces for the services I work with most
a list of links of “typical” or “exemplar” things
- links to our internal tool views for typical payments, merchants, etc
- typical size (in bytes) of various protobuf messages we use a lot, size of 1M messages, #messages in 1MB/GB
common coding idioms, like several variants of @RunWith that we use in various cases in our test code.
useful commands for doing stuff (curl/SQL/plain old shell)

Plain text is great for all the reasons it usually is. But it’s especially useful here (see what I did there?) because the file loads much faster than Google Docs or wiki pages, it’s grep-able, it’s trivial to copy to a new machine, there’s no fuss about futzing with the document to get it to format properly, and soforth.

launchd as cron crash course

Fri, 08 Aug 2014 00:00:00 +0000

insert

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>com.whatever.five_after</string>
        <key>ProgramArguments</key>
        <array>
                <string>echo just ran > /tmp/whatever_five_after</string>
        </array>
        <key>StartCalendarInterval</key>
        <dict>
                <key>Minute</key><integer>5</integer>
        </dict>
</dict>
</plist>

into $HOME/Library/LaunchAgents/com.whatever.five_after.plist

If you call a script in the ProgramArguments section, remember to make it executable and define the script properly.

Run

launchctl load $HOME/Library/LaunchAgents/com.whatever.five_after.plist
launchctl start com.whatever.five_after

Can also run every N seconds with

<key>StartInterval</key><integer>N</integer>

Can also check the status with

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])

some setup notes

Sun, 27 Oct 2013 00:00:00 +0000

zsh

Zsh is an amazing (mostly) drop-in replacement for bash.

On OSX, just run

> brew install zsh

You also want to install oh-my-zsh.

I went a little crazy with plugins. My list is:

plugins=(autojump brew git git-flow gnu-utils gpg2 osx textmate zsh-syntax-highlighting history-substring-search)

SSH

I ssh a lot. So I have a bunch of host entries in my .ssh/config file. Each looks like:

Host [shortname]
     Hostname [hostname]
     User     [username for hostname]
     IdentityFile [my home directory]/.ssh/[id_rsa file for this host]

You also need identity files for hosts you use. I tend to use a different one on each host I connect to; some might consider this overly paranoid. Probably it’d be better to use 1 key but only for a shorter period of time. In any case, you need to use

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:

cplex matlab interface

Wed, 01 Feb 2012 00:00:00 +0000

Just for my own reference, I’m documenting the interface to CPLEX.

CPLEX expects a problem in the form ( \begin{split} \min \qquad & g^Td + \frac12 d^TWd\ \text{subject to} \qquad & c_L \leq Ad \leq c_U\ & d_L \leq d \leq d_U \end{split} ) and is called by

cplex = Cplex('test');
cplex.Param.feasopt.tolerance.Cur = 1e-8;
if params.printLevel < 8
    cplex.DisplayFunc = [];
end
cplex.Model.sense = 'minimize';
cplex.Param.qpmethod.Cur = 1;
cplex.addCols(gk,[],bl-xk,bu-xk);
cplex.addRows(-ck, A0, -ck);
cplex.Model.Q = W;
cplex.Model.obj = g;
cplex.Model.lb = d_L;
cplex.Model.ub = d_U;
cplex.Model.lhs= c_L;
cplex.Model.rhs= c_U;
cplex.solve();

Getting GnuPlot to compile on OSX

Thu, 27 May 2010 00:00:00 +0000

I misunderstood an officemate’s question yesterday and set out to compile gnuplot. Stock GNUPlot will fail to compile on OSX due to an incompatibility in the readline library. So when you compile, let GNUPlot know to use the one included:

> tar xzvf gnuplot*
> cd gnuplot-4.2.39
> ./configure --prefix=/usr/local --with-readline=builtin
> make
> sudo make install

Pylab PDF

Tue, 25 May 2010 00:00:00 +0000

I’m in the process of kicking the MATLAB habit and replacing it with Python. Pylab is a reasonable approximation to the 2D plotting capabilities of MATLAB, but by default Pylab doesn’t run on headless(ie, non-GUI) boxes. So on my macbook, where I’m often running things interactively, I have

backend : macosx

and on the faster core2quad machine I send off longer-running jobs to, I used

backend : PDF

in the .matplotlib/matplotrc file.

MySQLdb module in Python on Ubuntu

Sat, 30 May 2009 00:00:00 +0000

To install the mysqldb module in python on Ubuntu:

sudo apt-get install python-mysqldb

A Quick MySQL Reference

Wed, 27 May 2009 00:00:00 +0000

I got frustrated with not being able to write MySQL because I don’t do it often enough to be seeing it in my nightmares like MATLAB. But recently my datasets got annoyingly huge and it seemed like SQL might be a boon to me. So I set out to write a quick little program, and ended up writing this little reference along the way.

Also, Sharvil Shah contributed some comments to it, so thanks to him for that!