Saturday, September 29, 2007

Subplot with polar

If you want to do a polar plot in a subplot you will be surprised -
when you do subplot(1,2,1) (say) this sets up the axes in cartesian mode. You need to do

subplot(1,2,1,polar=True) to set the plot in polar mode

Wednesday, September 26, 2007

Monday, September 24, 2007

Setting up SVN repository on a linux machine

Refer to SVN manual at http://svnbook.red-bean.com/en/1.0/svn-book.html

What worked for me:

repositories created by
svnadmin create /path/to/repo/module

initial import via svn import module file:///path/to/repo/module -m "initial import"
make sure you have the following subdirectories in this initial folder that you import
trunk (all the code goes here)
tags (empty)
branches (empty)

local checkout:
svn checkout file:///path/to/repo/module/trunk module
Tortoise CVS checkout repository URL like:
svn+ssh://user.name@machine.name/path/to/repo/module/trunk

User management for svn repositories
Initial setup:
groupadd svnusers #add a new group for svnusers
chgrp svnusers repo/ -R #repo is now under svnusers
chmod g=swrx repo/ -R #the directory tree is now writable by group

For each new svnuser with write access:
usermod -a -G svnusers newuser #add newuser to the svnusers group
id newuser #make sure it took

Rescind SVN write permission from a user
gpasswd -d newuser svnusers

Blender saga Part II

I used blender to make some 3D models that want to fabricate. When I went to do that today at the Device Realization lab, we found that the model was only displaying as a wireframe, with the faces not filled in. I checked with the free viewer from Myriad and the models seemed fine. I found this page that lists some free stl viewers.

Saturday, September 22, 2007

Why you should hold the bow with an open grip

Today, while shooting some ends with my new bow, I finally figured out the major reason why archers are told to shoot with an open grip. I read stuff about vibration and shock etc., but I think the real reason has to do with how the string is pulled. As you pull the string you need to pull it perpendicular to the plane of the bow. If you hold the bow in a tight grip you can potentially pull the string to one side, rather than straight back. This will impart a lateral component to your arrow release, causing a lot of fish-tailing. If you use an open grip, no matter how you pull the string the bow will yaw so that the limbs are perpendicular to the pull. This will reduce fish tailing.

Wednesday, September 19, 2007

Use feathers for shooting off the shelf

From what I read, the feathers are softer, so they collapse easily when they hit the shelf and affect arrow direction less.

Monday, September 17, 2007

Backstroke of the west OR Gained in translation

A pirated version of "The revenge of the sith" apparently gained something in translation. This website has a list of screenshots from a Star Wars III DVD bought in china with hilarious closed captioning.

The title itself "Revenge of the Sith" has the interesting translation "Backstroke of the west", leading me to all sorts of conspiracy theories of how in Totalitarian China, the evil empire in Star Wars is called "The West"

Saturday, September 15, 2007

Making a model using blender

Well written tutorials and documentation are found on the wiki.

Some tips:
  • Blender's top "menu bar" can be resized by dragging down, to reveal a preferences menu (Enable auto save on this menu, while you are at it)
  • BUG: Blender 2.44 on windows, boolean operation : union is actually difference and vice versa
  • Copying an object from one file to another (or even the same file). Remember: go into the 'OBJECT' subtree.
  • Export to STL: Remember: blender exports the currently selected object.

Keyboard short cuts:

tab - switch between object and edit mode
a - toggle between select all and select none
b - box select, select a bunch of vertices by dragging
e - extrude
g - grab
m - move object to layer dialog box
s - scale
w - boolean operation menu
shift-k - scissors

Friday, September 14, 2007

Bessel functions

From a hint here, we find that we need scipy.special

import scipy.special as ss

n = 2 #order of bessel function
x = 4 #evaluated at x = 4
y = ss.jn(n,x)

Wednesday, September 12, 2007

Web frameworks with python

I was writing a tutorial for SNAIU when I started to wonder what facilities Python has for writing browser based GUIs. I know that R has Rweb. I have had a great experience with Ruby On Rails, writing RRiki to handle my note taking and reference management needs. So I started to look into what Python has by way of web frameworks.

The python wiki has two relevant pages: web frameworks and web programming. I was attracted to Pylons, because it was the closest to Rails. But for my app what I need is something closer to Rweb, where you can create webpages with links that call actual code and return results on the webpage itself. A browser based GUI!

If anyone knows of any such solution, please tell me. Meanwhile, I think Pylon is the closest I can think off.

2007.11.1 - and then I discover SAGE. It looks like Rweb enhanced. Looks very promising.

Archery quick tips

Some factoids/tips I found useful (and which may not apply to you!)
  1. A toxophilite is a person who is devoted to archery
  2. A right hand bow is held in the left hand and shot by a right eye dominant person
  3. An adult taking up archery should start with a 30# or less bow
  4. For target archery a bow with 30-40# is sufficient
  5. For target archery 75gr points are sufficient
  6. A longer bow is more stable. For a medium height person a 62-66" bow is recommended
  7. Bow poundages are measured at 28" draw
  8. Drop-away arrow rests are meant for compound bows, not recurves, which use at most a plunger.
  9. Outdoor target archery ranges are from 30m to 90m

Resources for begining recurve archery

I took up archery with instruction books, rather than an instructor. Time will tell if that was smart. I read a lot of stuff from websites and some from books. In the UMD library I could not find an archery book more recent than some time in the 1970s ! I guess UMD is not big into archery!

I read the following books:

"Shooting the Bow", Larry C. Whiffen, The Bruce Publishing Co, Milwaukee 1946.
This is an instructional book with charming mid-20th century black and white pictures written in a charming and humorous mid-20th century style. It has hand illustrations for stance, grip etc. It has a one page chapter about correcting errors.

"Archery", Lorraine Pszczola, W.B. Saunders Co, 1976
This is meant as an instructional booklet for college/school archery programmes. Filled with illustrations about stance, and grip etc.

"Archery for beginners", John C. Williams, Contemporary Books, 1976
This was the one I referred to the most. The archers in bellbottoms are a hoot. It also uses the words "sexy" and "groove". A true 70s book. It has some good advice about correcting errors.

My favorite book of these three is Williams' book because the advice on stance, grip and release are very well described and illustrated with photographs. Williams also explains the mechanics behind it all, which makes his writing more aesthetically pleasing foe me.

It helped me to read several books because there were differences in the material and advice, and I picked out those things that struck me as useful, or that helped me. There was contradictory advice about stance and grip, which illustrated to me that there is not ONE way to shoot an arrow!

Mostly it was the illustration and pictures that helped me from the books. A lot of text about archery is available on the web. Unfortunately a lot of the websites don't have pictures, so that's where you have to refer to the books.

Some websites that I find useful are:


Oh, and here are some things I found useful.

Sunday, September 9, 2007

Regular expressions in SciTE

From the SciTE's documentation webpage, you need to check 'Regular expression' in the search dialog box, and then the regex parts of your search will be demarcated by \( and \). For example, to replace all occurences of AUTO_INCREMENT=??? where ??? is some number by nothing, you would set the Find box to be AUTO_INCREMENT=\([0-9]+\) and the Replace box would be untouched.

Thursday, September 6, 2007

Archery

I took up archery recently, and I have really gotten into it. I've added some archery related links on the blog.

I started out cheap, since I was interested in it enough to want to buy equipment, but I didn't know if it would be a hobby that would stick.

No-brand fibreglass recurve bow 60", 30-35# pull at 28" -- $50 (esportsonline)

Shooting glove -- $10
Quiver -- $10
Arm guard -- $10
6 carbon express thunderstorm arrows -- $34
Points 75gr and 125gr - $12 total - (all from Basspro)

Total approx $125

The closest basspro shop did not carry cheap recurves (they were all selfbows, and looked very nice and something you would hang over your fireplace and cost something like $500). They carried a lot of compounds, and a few recurves for children (54" high and 9lbs draw). I found more stuff online.

Basspro is fine for most things and esportsonline service is fine.

The no-name recurve bow I got is an OK starter. It's a generic kind of ambidextrous bow that you are likely to find in a number of places. The arrows I got have spines for bows from 30-50#. They are mangled by the bow. The fletching brushes past the riser (Its NOT centershot, because of the ambidextrous design) and two vanes have picked up a black coat from the riser. Those vanes have also been damaged a bit by this brush past.
Other than this, I would say the bow is OK. My shots arn't consistent, and I can't say if that if my form or the bows fault.

If anyone is looking for a decent starter bow I would recommend looking for a center shot one.