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Jan 14
making a new command in latex tex, use-this-code
Yep, it’s totally trivial, but I always forget how to create a new command in latex that has arguments. Here it is once and for all. 
\newcommand{\err}[1]{\textcolor{red}{#1}}
Jan 4
communicating between apps use-this-code
ZeroC comes recommended as a way to communicate between different applications / processes.
Dec 10
testing for a valid float in ruby ruby, use-this-code
Here’s a nice patch to the string class in Ruby to test if a string represents a valid floating-point number: 
class String
  def valid_float?
    true if Float self rescue false
  end
end
Oct 20
ruby 1.9 enumerable methods in 1.8 ruby, use-this-code
Ruby 1.9 has some nice new methods on the Enumerable class; for example, each_cons, which iterates through consecutive slices of an array. You can add these to Ruby 1.8 with 
require 'enumerator'
Jul 30
determining png image size in ruby ruby, use-this-code
Short, simple and sweet. Found here, which reports that it’s attributable to Sam Stephenson. 
IO.read('image.png')[0x10..0x18].unpack('NN')
May 21
enumerate in python (again) python, use-this-code
I wrote down below about enumerate, which lets you access (index, item) pairs within a loop. I guess I thought it was a good idea, because I was about to write it here again. If you need both the index and item from a list, use enumerate: 
for index, item in enumerate(items):
    pass
I haven’t used it in the intervening two months, but oh well.
Jul 31
sample from a discrete distribution in matlab math-ish, use-this-code
Sampling from a discrete distribution, where p is a vector of probabilities: 
min(find(rand() < cumsum(p)))
Jul 21
a few code snippets for timing in C c, use-this-code
First, tic() and toc() functions. These work like Matlab: tic() starts the timer, and toc() stops it and gives formatted output. There’s also a tocq() function which just returns the number of elapsed seconds. 
#include <time.h>
static clock_t tic_timestart;

void tic(void) {
   tic_timestart = clock();
}

float toc(void) {
   clock_t tic_timestop;
   tic_timestop = clock();
   printf("time: %8.2f.\n", (float)(tic_timestop - tic_timestart) / CLOCKS_PER_SEC);
   return (float)(tic_timestop - tic_timestart) / CLOCKS_PER_SEC;
}

float tocq(void) {
   clock_t tic_timestop;
   tic_timestop = clock();
   return (float)(tic_timestop - tic_timestart) / CLOCKS_PER_SEC;
}
A bit of code for counting flops: first, a statistics structure, then some defines. 
/* CFDIV    divides             1/a[3]
* CFADD    adds                c[12] + d[12]
* CFMUL    multiplies          b[4] * h[7]
* CFASN    assigns             A[5] = 0
* CFSTO    stores              A[5] = (...)
* CFTFR    transfers           A[5] = b[7]
* CFNTF    negated transfers   A[5] = -b[7]
* CFCOM    compares            c[5] < b[7]
*/
typedef struct statistics_t *statistics;
typedef struct statistics_t {
   long div;
   long add;
   long mul;
   long asn;
   long sto;
   long tfr;
   long ntf;
   long com;
} Statistics;