static field shared between instances of generic

The documentation says that one implementation is shared. I guess it makes sense this translates to one copy of the class variables getting shared as well.

public class GenericStatic<T> {
    static String o = "";
    String oo() {
 return o += "o";
    }

    public static void main(String[] args) {
 GenericStatic<Object> a = new GenericStatic<Object>();
 GenericStatic<String> b = new GenericStatic<String>();
 System.out.println(a.oo());
 System.out.println(b.oo());
    }
}

$ javac GenericStatic.java
$ java GenericStatic
o
oo

R: keeping a 1-d subset of a matrix a matrix

By default, if a subsetting operations yields a one-dimensional matrix (row or column vector), the dimensions are dropped.

> (m <- matrix(1:4, nrow=2))
     [,1] [,2]
[1,]    1    3
[2,]    2    4
> (v <- m[1, 1:2])
[1] 1 3

This can cause problems when we want to go ahead and continue using the result in matrix operations:
> v %*% m %*% t(v)
Error in v %*% m %*% t(v) : non-conformable arguments

The solution is to explicitly tell R not to drop the dimensions:

> (v <- m[1, 1:2, drop=FALSE])
     [,1] [,2]
[1,]    1    3
> v %*% m %*% t(v)
     [,1]
[1,]   52

Something else to look at: removing a column, given its name in a variable: Chris Handorf, subsetting a dataframe

printf("%02d", n)

irb(main):005:0> printf "%02d\n", 3
03
=> nil
irb(main):006:0> printf "%02d\n", 13
13
=> nil
irb(main):007:0> printf "%02d\n", 113
113
=> nil
Use printf to format numbers, filling in with zeros for 1 digit numbers. *
(This is Ruby but I'm marking this as C since that's where I'm most likely to end up using it.)

get flat output in Maxima

I think I've written before this before but a search didn't turn it up. This just concerns getting "flat", all-on-one-line, non-fancy ASCII output from Maxima. (This is especially useful when the output is destined to be converted into C code.)

(%i8) display2d: false$
(%i9) %e^t;

(%o9) %e^t
(%i10) display2d: true$
(%i11) %e^t
;
                                        t
(%o11)                                %e

Speaking game using python and Mac OS X's say

#!/usr/bin/env python

import os
import random

def say(word):
    os.system("say " + word)

class Score:
    def __init__(self):
 self.total = 0
 self.correct = 0

if __name__ == '__main__':
    pairs = [["bed", "bad"], ["sped", "speed"],
      ["wary", "very"], ["bull", "ball"],
      ["mall", "mole"], ["pale", "pull"],
      ["soup", "stoop"], ["file", "fill"]]
    scores = {}
    for pair in pairs:
 scores["".join(pair)] = Score()
    input = ""

    print("To quit, enter q")
    while input != "q":
 pair = random.choice(pairs)
 word = random.choice(pair)
 print("1) " + pair[0])
 print("2) " + pair[1])
 say(word)
 input = raw_input("What did the computer say?: ")
 input = input.strip()
 
 if input != "q":
     key = "".join(pair)
     score = scores[key]
     score.total += 1
     if input == word:
  score.correct += 1
  print("Correct!")
     else:
  print("Wrong!")
     print("You\'ve gotten the right answer for "
    + " vs ".join(pair) + " "
    + str(score.correct) + " out of "
    + str(score.total) + " times")

Here's a little game to drill you on somewhat similar sounding pairs of English words. I'm sure much could be done to improve it. Is the use of a class here kosher with Python practice? What's contrary to idiom here?

simulate from AR (and general ARIMA)

> RSiteSearch("generate arima") #~~~~~~~($$$)
> layout(matrix(1:2))
> a1 <- ar(y)
> y1 <- arima.sim(list(ar=a1$ar), 9600)
> plot(y1, type="l")
> a2 <- arima0(y, order=c(10, 0, 5))
> y2 <- arima.sim(list(ar=a2$coef[1:10], ma=a2$coef[11:15]), 9600)
> plot(y2, type="l")

printing an array in gdb

(gdb) p *(bestSplit->param->mu)@9
$6 = {0, 0, 0, 0, 0, 0, 0, 0, 0}
(gdb) p *(bestSplit->param->p)@(bestSplit->param->numClusters)
$8 = {0, 0, 0, 0, 0, 0, 0, 0, 0}

Just what I've been dreaming of! The syntax: "*" <array name> "@" <number of elements>. See Debugging with GDB -- Arrays