Diary

Reasonable Contour Levels

import math
def generateContours(min_value, max_val, target):
    value_range = max_val - min_value
    x = int(round(3 * math.log10(value_range / target)))
    if x % 3 == 1:
        x = 2.5 * math.pow(10,math.floor(x / 3))
    elif x % 3 == 2:
        x = 5.0 * math.pow(10,math.floor(x / 3))
    else:
        x = math.pow(10, x / 3)
    low = math.ceil(min_value / x) * x
    return [low + (x * i)
        for i in xrange(1+int(value_range / x))]

Collapse paragraphs

#!/usr/bin/env python
# ignores witespace
# collapses paragraphs
import sys
for line in sys.stdin:
    line = line.strip()
    if len(line) == 0:
        sys.stdout.write('\n\n')
    else:
        sys.stdout.write(line+' ')

generate image files

#!/usr/bin/python

import Image
import numpy

X = 1024
Y = 768
filename = '/tmp/x.png'

ima = numpy.zeros((Y,X,4), dtype=numpy.uint8)
ima[:,:,3] = 255 # make opaque
Image.fromarray(ima,mode='RGBA').save(filename)

colapsing multiple for loops

#!/usr/bin/env python

import glob, sys

def globlist(l):
    return (j for i in l for j in glob.iglob(i))

for filename in globlist(sys.argv[1:]):
    print filename

makefiles

# Example (GNU) Makefile for a C++ project.
# Assume there is a .h file for each .cxx

executable_file_name = program
cxxfiles = \
  file_one.cxx \
  file_two.cxx \
  file_three.cxx \
  file_four.cxx

CXX = g++
CXXFLAGS = -g -Wall -std=c++0x
objects := $(cxxfiles:.cxx=.o)
headers := $(cxxfiles:.cxx=.h)

##  If you use other extensions:
# objects := $(cxxfiles:.cpp=.o)
# objects := $(cxxfiles:.cc=.o)
# headers := $(cxxfiles:.cxx=.hh)

.PHONY : clean all
all : $(executable_file_name)
$(executable_file_name) : $(objects)
	$(CXX) $(CXXFLAGS) $^ -o $@
%.o: %.cxx $(headers)
	$(CXX) -c $(CXXFLAGS) $< -o $@
clean:
	rm -f -v $(objects)

# Example (GNU) Makefile for a Java project.
# Constructs a JAR file with all of the classes.

entrypointclass = Program
jarfile = program.jar
javafiles = \
  file_one.java \
  file_two.java \
  file_three.java \
  file_four.java

JAVAC = javac
JAVA = java
JAR = jar
RM = rm -f
JCFLAGS = -Xlint -g
JFLAGS = -enableassertions
classes := $(javafiles:.java=.class)

.PHONY : clean all run
all: $(jarfile)
run: $(jarfile)
	$(JAVA) $(JFLAGS) -jar $(jarfile)
clean:
	$(RM) -v $(classes)
$(jarfile): $(classes)
	$(JAR) cvfe $@ $(entrypointclass) $^
%.class : %.java
	$(JAVAC) $(JCFLAGS) $^

rosetta stone

PyQt QInputDialog.get*() wrappers

#!/usr/bin/env python

import PyQt4.QtGui

def getInt(title, label, mini=-2147483647, maxa=2147483647):
  assert mini <= maxa
  default = min(max(0, mini), maxa)
  (ret, ok) = PyQt4.QtGui.QInputDialog.getInt(
    PyQt4.QtGui.QWidget(), title, label, default, mini, maxa)
  if not ok:
    raise Exception('select error')
  return ret

def getItem(title, label, items):
  (ret, ok) = PyQt4.QtGui.QInputDialog.getItem(
    PyQt4.QtGui.QWidget(), title, label, items)
  if not ok:
    raise Exception('select error')
  return str(ret)

def getFloat(title, label, mini=-2147483647, maxa=2147483647,
       default=None, decimals=1):
  assert mini <= maxa
  if default is None:
    default = min(max(0, mini), maxa)
  (ret, ok) = PyQt4.QtGui.QInputDialog.getDouble(
    PyQt4.QtGui.QWidget(), title, label, default, mini, maxa, decimals)
  if not ok:
    raise Exception('select error')
  return ret

def getItem(title, label, items):
  (ret, ok) = PyQt4.QtGui.QInputDialog.getItem(
    PyQt4.QtGui.QWidget(), title, label, items)
  if not ok:
    raise Exception('select error')
  return str(ret)

def getText(title, label, default=''):
  (ret, ok) = PyQt4.QtGui.QInputDialog.getText(
    PyQt4.QtGui.QWidget(), title, label,
    PyQt4.QtGui.QLineEdit.Normal, default)
  if not ok:
    raise Exception('select error')
  return str(ret)

qApplication = PyQt4.QtGui.QApplication([])

print getItem('getItem()', 'select a color',
  ['red','orange','yellow','green','blue','violet'])
print getInt('getInt()', 'give me a number', 0, 100)
print getFloat('getFloat()', 'give me a number', 0.0, 1.0, None, 2)
print getText('getText()','give me some text','string')

Java Makefiles

Here's a basic makefile for compiling Java programs. On most systems, you will only need to edit the first three lines.

classes = Prog.class AnotherClass.class
entrypointclass = Prog
jarfile = program.jar

JAVAC = javac
JAVA = java
JAR = jar
RM = rm -f
JCFLAGS = -Xlint -g 
JFLAGS = -enableassertions

.PHONY : clean all run
all: $(jarfile)
run: $(jarfile)
	$(JAVA) $(JFLAGS) -jar $(jarfile)
clean:
	$(RM) -v *~ $(classes)
$(jarfile): $(classes)
	$(JAR) cvfe $@ $(entrypointclass) $^
%.class : %.java
	$(JAVAC) $(JCFLAGS) $^

One can start an executable with arguments inside GDB with a single bash command:

$ gdb EXECUTABLE <<< 'run ARG1 ARG2 ARG3'

Quick linear regression script

#!/usr/bin/env python
#sudo yum -y install scipy
# input is space-deleimited (x y) pairs.
import scipy
import numpy
import sys

inp = [map(float, l.split()[0:2]) for l in sys.stdin]
x = numpy.array([t[0] for t in inp])
y = numpy.array([t[1] for t in inp])
fit = scipy.polyfit(x,y,1)
print 'y = (%f) x + (%f)' % tuple(fit)

power fit:

#!/usr/bin/env python
#sudo yum -y install scipy
# input is space-deleimited (x y) pairs.
import scipy
import numpy
import sys
import math
inp = [map(math.log, map(float, l.split()[0:2]))
	for l in sys.stdin]
x = numpy.array([t[0] for t in inp])
y = numpy.array([t[1] for t in inp])
fit = scipy.polyfit(x,y,1)
print 'y = ({0[1]})e^({0[0]})'.format(tuple(fit))

This script will snap your window to the left or right side of the screen in Linux: (SOURCE)

#!/bin/sh
## ${HOME}/bin/wmctrl-snap-edge
#DTPD#
WMCTRL="${HOME}/bin/wmctrl_`arch`"
#WMCTRL="/usr/bin/wmctrl"
test -x "/usr/bin/xdpyinfo" -a -x "$WMCTRL" || {
    echo "error"; exit 1; }

WIDTH=`xdpyinfo | sed -n 's/ *dimensions: *\([0-9]*\)x.*/\1/p'`
HALF=$(($WIDTH / 2));
"$WMCTRL" -r :ACTIVE: -b add,maximized_vert;
if test "$1" = "left" ; then
	"$WMCTRL" -r :ACTIVE: -e 0,0,0,$HALF,-1
elif test "$1" = "right" ; then
	"$WMCTRL" -r :ACTIVE: -e 0,$HALF,0,$HALF,-1
fi

If you don't have wmctrl installed, you can apt-get it (Ubuntu):

sudo apt-get --yes install wmctrl

sudo yum install libXmu-devel
cd /tmp
wget 'http://tomas.styblo.name/wmctrl/dist/wmctrl-1.07.tar.gz'
tar --extract --gzip --file "wmctrl-1.07.tar.gz"
cd wmctrl-1.07
./configure
make -j 4
mv wmctrl ${HOME}/bin/wmctrl_`arch`

The next step is to set up hotkeys. If you use Metacity like I do, then:

gconftool-2 --type string --set \
	/apps/metacity/global_keybindings/run_command_6 \
	'<Ctrl><Alt>Page_Up'

gconftool-2 --type string --set \
	/apps/metacity/keybinding_commands/command_6 \
	"${HOME}/bin/wmctrl-snap-edge left"

gconftool-2 --type string --set \
	/apps/metacity/global_keybindings/run_command_7 \
	'<Ctrl><Alt>Page_Down'

gconftool-2 --type string --set \
	/apps/metacity/keybinding_commands/command_7 \
	"${HOME}/bin/wmctrl-snap-edge right"

#!/bin/sh
# Restart X11 under Ubuntu. #
#DTPD#
test `id -u` = "0" || exec sudo "$0"
exec /usr/sbin/service gdm restart

(defun next-good-buffer () "HWC" (interactive)
  (next-buffer)
  (while (and (not (string= (buffer-name) "*scratch*"))
	      (equal (buffer-file-name) nil))
    (next-buffer)))
(defun previous-good-buffer () "HWC" (interactive)
  (previous-buffer)
  (while (and (not (string= (buffer-name) "*scratch*"))
	      (equal (buffer-file-name) nil))
    (previous-buffer)))

(global-set-key [(control next)] 'next-good-buffer)
(global-set-key [(control prior)] 'previous-good-buffer)
(global-set-key [(control tab)] 'next-good-buffer)
(global-set-key [(control shift tab)] 'previous-good-buffer)
(global-set-key [(control iso-lefttab)] 'next-good-buffer)
(global-set-key [(control shift iso-lefttab)] 'previous-good-buffer)

.emacs look and feel

;_____________________________________________________________________
;
;	 Look And Feel
;_____________________________________________________________________
(setq inhibit-startup-screen 't)
(tool-bar-mode nil)
(menu-bar-mode nil)
(set-scroll-bar-mode 'right)
(when window-system
  (add-to-list 'default-frame-alist '(background-color . "black"))
  (add-to-list 'default-frame-alist '(foreground-color . "white"))
  (add-to-list 'default-frame-alist '(background-mode . dark))
  (custom-set-faces '(default ((t
    (:height 110 :family "DejaVu Sans Mono"))))))

;_____________________________________________________________________
;
;	 Keyboard Bindings
;_____________________________________________________________________
(setq x-select-enable-primary t)
(setq x-select-enable-clipboard t)
(cua-mode)
(global-unset-key (kbd "M-z"))
(global-set-key (kbd "M-z") 'suspend-emacs)
(global-set-key (kbd "C-h") 'backward-delete-char-untabify)
(global-set-key	[(control s)] 'save-buffer)
(global-set-key	[(control f)] 'isearch-forward)
(define-key isearch-mode-map [(control f)] 'isearch-repeat-forward)

One can make a hostname alias for SSH and SCP by adding to the the SSH config file:

##  ~/.ssh/config
Host cs
	HostName = login.cs.unc.edu
	User = hal

make -j

Update: Russ reccomends 2N threads.

#!/bin/sh
## {$HOME}/bin/makej
renice 1 $$ > /dev/null
N_CPUS=`grep processor /proc/cpuinfo | wc -l`
N_THRDS=`expr ${N_CPUS:-1} "*" 2`
exec /usr/bin/make -j "$N_THRDS" "$@"

#!/bin/sh
N_CPUS=`grep processor /proc/cpuinfo | wc -l`
exec /usr/bin/make -j "$N_CPUS" "$@"

yet another emacs function

(defun diary () (interactive)
  (let ((ddir "d:/")
        (year (format-time-string "%Y"))
        (ymd (format-time-string "%Y-%m-%d"))
	(ymdt (format-time-string "%Y-%m-%d %H:%M:%S %z")))
    (make-directory (concat ddir year ) 't)
    (find-file (concat ddir year "/" ymd ".txt"))
    (goto-char (point-max)) (newline)
    (insert  ymdt) (newline) (newline)))

stopwatch

#!/usr/bin/python
"""Stopwatch program.

Hit 'Enter' to save a time.

Hit 'Ctrl-c' to stop the script
"""
from datetime import datetime, date, time
import time, sys
start = datetime.now()
print __doc__
try:
	while True:
		time.sleep(0.071)
		sys.stdout.write('\b'*22)
		sys.stdout.write(str(datetime.now() - start))
		sys.stdout.flush()
except KeyboardInterrupt:
	sys.stdout.write('\n\n')

diagnose

I'm only using one out of four processor cores for this batch job. Why is my computer slowing down? Ohhh. Memory leak. That's easy to remedy.

out of town

I'll be at MSU the next two weeks.

sync

One beautiful thing about git is that I can clone my own clone of someone else's repository. That way I can easilly keep my laptop in sync with my workstation. Neat.

reduce

In high-school chemistry, you learn that the ideal gas law is

These letters are drilled into my head, but I realised yesterday that I am losing my intuitive understanding of the relation. The physics version of it is

where N is now a dimensionless number and k is comes from the definition of T. Let ρ be our number density and the relation simplifies to

Pressure is density times temperature.

In the heterogeneous CS Unix environment, I may be executing emacs from a console as “emacs -nw” or from an icon on the desktop. Some computers will have the emacs-color-theme package installed, others won't. So in my .emacs file, I put the following lines:

;; from .emacs ...
(setq emacs-style-file "~/.emacs-style")
(when
    (and window-system
         (require 'color-theme nil t)
         (file-readable-p emacs-style-file))
  (progn
    (load emacs-style-file)
    (my-color-theme)))

After two weeks, I've finally produced a proof of concept. Not an important program, and it's not finished, but I feel like I've made something.

GNU tar for win32 can't actually fork a process for gzip. What century is it? Here's my fix:

@echo off
REM untargz.bat
:AGAIN
if "%1" == "" goto END
gzip -d -c < "%1" | tar -xv
shift
goto AGAIN
:END

Big ice cubes melt more slowly than small ones. Are your ice cubes big enough?

Just becasue Samba and AFS allow you to open multi-gigabyte data files as if they were local, you still should not. Even if you have a nice 100 Mbit/sec direct connection. Unless the software in question knows to expect these sort of shenanigans.