Mailman 3 May 2007 - Edu-sig

Tomorrow's Python Class
by kirby urner May 5, 2007

May 5, 2007

My course is taking on a "how it works" aspect, looking at two topics of interest to most teenagers: computer games and animated movies. I'm explaining how the games need real time computations to keep the frame rate high, while the movies render frame by frame, taking hours if need be, only to give a real time, non-interactive experience at runtime. My technologies for illustrating these two different approaches to computer graphics: VPython for real time with a frame rate; POV-Ray for rendering animations. Python sits in the driver's seat vis-a-vis both of these engines. More mathematically speaking, I'm finding a lot to recommend a Vector class as a kind of anchoring concept, a foot in the door if you will. Having explored Dog and Monkey, maybe Human, as subclasses of Mammal, with attention to dot notation and special names such as __init__ and __repr__, I think they're ready for something more abstract that nevertheless has a visual representation. My default background color for the VPython window is cyan, which looks a little like sea water in a coral lagoon. So I talk about "the fish tank" or "the aquarium" quite a bit (which might invoke images of 'Shark Tale' in some of our savvy viewers). That gives the feeling of volume or space. It's not a flat window, but a tank. My Vector class includes the following simplification, which you can actually find in some linear algebra texts: vectors always tail-originate at the origin. If you want an edge that connects any two points, neither of them (0,0,0), well, that's what we call an Edge, and two vector tips define it. So how do we define polyhedra i.e. shapes in general then? I go with a wireframe view to start, and require two data structures: a dictionary of vectors (tails at (0,0,0)), and a list of face tuples, each element going around a face, either clockwise or counter-clockwise. So, for example, a Tetrahedron (subclass of Polyhedron) requires a dictionary of four vertices {'a':Vector((x0,y0,z0)), 'b':Vector((x1,y1,z1)), 'c':Vector((x2,y2,z2)), 'd':Vector((x3,y3,z3))} and a list of four face tuples: [('a','b','c'), ('a','c','d'), ('a','d','b'),('b','c','d')] Those of you already into computation geometry (CG) will recognize that I'm not doing anything very original here. The widely used OFF format, plus VRML, are quite similar, in giving a list of points (what I'm calling vectors) and a list of faces consisting of points, going around each face. Exactly my approach as well. Back to the Vector class, my approach with VPython has been to wrap the native visual.vector in a class of my own design. I implement __add__ and __mul__ for vector addition and scalar multiplication respectively. __neg__ returns a vector 180 degrees from the current one (e.g. newv = - oldv). Then I have dot product and cross product, which I wouldn't insist on using initially. __sub__ may be defined as "adding the additive inverse of" i.e. __add__ the __neg__ of some other vector to this one... I'm going in to such detail because I don't think these will just be the idiosyncratic choices of a lone wolf independently operating gnu math teacher. Other gnu math teachers will likely find this is just the right mix of newfangled and traditional. We've been teaching Gibbs-style vectors for several decades to high schoolers (it's a part of the IB curriculum as well as most slightly accelerated USA/UK maths). Now that computers are in the picture, and uncluttered agiles like Python, I think we're ready to rethink this whole segment, and do something that's fun for a change (not to mention more job relevant than ever). Sample IDLE session: IDLE 1.2 >>> from stickworks import Vector, Edge >>> thevector = Vector((1,1,1)) >>> othervector = Vector((2,-1,1)) >>> thevector + othervector Vector @ (3.0,0.0,2.0) >>> 3 * thevector Vector @ (3.0,3.0,3.0) >>> - thevector Traceback (most recent call last): File "<pyshell#5>", line 1, in <module> - thevector TypeError: bad operand type for unary -: 'Vector' >>> thevector - othervector Vector @ (-1.0,2.0,0.0) Well well well, I see I haven't implemented vector negation. Time to pop the code and add it then... class Vector (object): """ A wrapper for visual.vector that expresses a cylinder via draw(), always pegged to the origin """ radius = 0.03 def __init__(self, xyz, color=(0,0,1)): self.v = vector(*xyz) self.xyz = xyz self.color = color self.cyl = None def draw(self): """define and render the cylinder""" self.cyl = cylinder(pos = (0,0,0), axis = self.v, radius = self.radius, color = self.color) def erase(self): """toss the cylinder""" if self.cyl: self.cyl.visible = 0 self.cyl = None def __repr__(self): return 'Vector @ (%s,%s,%s)' % self.xyz # some vector ops, including scalar multiplication def diff_angle(self, other): return self.v.diff_angle(other.v) def cross(self, other): temp = cross(self.v, other.v) return Vector((temp.x, temp.y, temp.z)) def dot(self, other): return dot(self.v, other.v) def __sub__(self, other): temp = self.v - other.v return Vector((temp.x, temp.y, temp.z)) def __add__(self, other): temp = self.v + other.v return Vector((temp.x, temp.y, temp.z)) def __mul__(self, scalar): temp = self.v * scalar return Vector((temp.x, temp.y, temp.z)) __rmul__ = __mul__ def __neg__(self): return Vector((-self.v.x, -self.v.y, -self.v.v)) >>> import stickworks >>> reload(stickworks) <module 'stickworks' from 'C:\Python25\lib\site-packages\stickworks.py'> >>> from stickworks import Vector, Edge >>> thevector = Vector((1,1,1)) >>> othervector = Vector((2,-1,1)) >>> -thevector Vector @ (-1.0,-1.0,-1.0) >>> -othervector Vector @ (-2.0,1.0,-1.0) Now maybe a teacher'd rather not *start* by wrapping a visual.vector inside this a class (like a candy wrapper). I could see doing a more generic Vector first, and just using it lexically, not graphically. VPython doesn't link the cylinder object to its vector in any tight way, and yet the cylinder makes the most sense as a visual representation. I add in a draw method such that thevector.draw() sticks a cylinder into the fish tank, with its tail at the origin. Until you explicitly *ask* for this graphical mode. If you look at my polyhedra.py, you'll see I wire up the Icosahedron based on three golden rectangles with sides phi and 1. That's explained more visually in my Feb 2000 'Getting Inventive with Vectors' piece, part of a 4 part numeracy + computer literacy series ( http://www.4dsolutions.net/ocn/numeracy1.html ). I actually keep these 3 mutually orthogonal golden rectangles available for VPython viewing, as a part of the Icosahedron class: class Icosahedron (Polyhedron): def __init__(self, verts = dict( # 12 vertices at the corners of 3 mutually # orthogonal golden rectangles xya=Vector(( phi/2, 0.5, 0.0)), # phi rectangle in xy xyb=Vector(( phi/2,-0.5, 0.0)), xyc=Vector((-phi/2,-0.5, 0.0)), xyd=Vector((-phi/2, 0.5, 0.0)), #----------------------------- xza=Vector((-0.5, 0.0, phi/2)), # Phi rectangle in xz xzb=Vector(( 0.5, 0.0, phi/2)), xzc=Vector(( 0.5, 0.0,-phi/2)), xzd=Vector((-0.5, 0.0,-phi/2)), #----------------------------- yza=Vector(( 0.0, phi/2, 0.5)), # Phi rectangle in yz yzb=Vector(( 0.0, phi/2,-0.5)), yzc=Vector(( 0.0,-phi/2,-0.5)), yzd=Vector(( 0.0,-phi/2, 0.5)), )): # 12 vertices self.vertices = verts # 20 equiangular triangles self.faces = ( ('xza','xzb','yza'), ('xza','xzb','yzd'), ('yza','yzb','xyd'), ('yza','yzb','xya'), ('xzc','xzd','yzb'), ('xzc','xzd','yzc'), ('xya','xyb','xzb'), ('xya','xyb','xzc'), ('xyd','xyc','xza'), ('xyd','xyc','xzd'), ('yzd','yzc','xyb'), ('yzd','yzc','xyc')) self.edges = self._distill() self.rectangles = ( ('xya','xyb','xyc','xyd'), ('xza','xzb','xzc','xzd'), ('yza','yzb','yzc','yzd')) def goldrects(self): Edge.color = green for r in self.rectangles: c0,c1,c2,c3 = [self.vertices[i] for i in r] Edge(c0,c1).draw() Edge(c1,c2).draw() Edge(c2,c3).draw() Edge(c3,c0).draw() [ http://www.4dsolutions.net/ocn/python/polyhedra.py ] Kirby

1 0

Re: [Edu-sig] interesting article about the future of user platforms
by Christian Mascher May 4, 2007

May 4, 2007

2 1

interesting article about the future of user platforms
by Laura Creighton May 4, 2007

May 4, 2007

http://worrydream.com/MagicInk/ I rather like the site name, too. :-) Laura Creighton

2 1

OLPC vs. CP4E
by kirby urner May 2, 2007

May 2, 2007

Just to clear up what might have seemed confusing, this editorial by John Dix in NetworkWorld (4.30.07 pg 26), other public sources, clears up a few things. === Cheap laptops: OLPC XO laptop: 433 MHz AMD Geode LX-700 x86 Processor, 256 MB RAM, 1GB NAND Flash storage, 3 USB Ports, 2w power usage during nominal load, 802.11b/g-based WiFi Mesh networking, Dual Mode Display 800X600 in color and 1200X900 in monochrome mode. Intel Classmate laptop: Celeron M processor at 900MHz, 7" 800 x 480 display, 256MB of DDR2 memory, 1GB of flash memory, 802.11b/g, GM915 graphics === According to John, Negroponte says 5000 X0s have been made, with a production rate of ~1 million/mo targeted for December of this year. Both models will run Windows, though XO's native platform is Sugar on Matchbox window manager on Linux. FORTH gets mentioned as a teaching language, not just Python. Some kids'll have Google accounts that back up everything centrally. As I've tried to make clear: my CP4E roadshow and teaching gigs aren't premised on any particular model of laptop and/or desktop, though I heartily welcome their advent, especially in the developing world. If an XO and/or Classmate shows up on my doorstep, I'll add it to my show and tell.[1] Until then, all I need is Python on any OS (IDLE works fine) plus some essential add-ons, such as VPython for OpenGL, PIL for stills, a few other bells and whistles (POV-Ray always a favorite), with Internet connectivity an obvious plus. But mostly what I need is access to a rich tradition of mathematics, which of course I've got [2], thanks to so many who've come before me in so many walks of life. I hope this clears up any lingering confusions about my recent postings. Kirby 4dsolutions.net/ocn myspace.com/4dstudios [1] example of a current rap: http://tinyurl.com/2elppl [2] http://www.4dsolutions.net/ocn/cp4e.html

2 4

Viztoyz Vid (high rez)
by kirby urner May 2, 2007

May 2, 2007

If you can spare the bandwidth, to the tune of a 35 meg .swf (Flash), I've published a version of the VizToyz vid that greatly exceeds the Google Video version in quality. And quality is what you need, when eyeballing source code. A lot of the Python screencasts on Youtube or whatever (including my own) are somewhat painful to watch, because the resolution is too low. And it's not the physical size of the screen that matters so much, e.g. iPods are rather easy on the eyes, even with Python source. Plus now there're new projectors, like we have for laptops, that'll take iPods in a slot (PJ258D ViewDock by ViewSonic). Looking forward to testing. So, the new CP4E resource: http://www.4dsolutions.net/ocn/python/viztoyz1/viztoyz1.html Kirby

1 0

OLPC (and a p.s. about Crunchy)
by Andre Roberge May 1, 2007

May 1, 2007

Some of you may remember my post http://mail.python.org/pipermail/edu-sig/2007-February/007771.html about the OLPC talk at Pycon. I seem to remember at the time that some people on this list expressed their desire to see this talk. A very similar talk is now available here: http://video.google.ca/videoplay?docid=-4285568518538296189&q=olpc+google+t… @Ivan K: if you are reading this message: great job!!! André ========== P.S. In my February post, I mentioned ** One open issue (as I understand it) is that of finding the "best practice" for plugins. The idea is that the core programs should be as small as possible but easy to extend via plugins.** Following this, and an email discussion with Johannes Woolard, I am glad to be able to say that "We" (read "Johannes") have now redesigned Crunchy so that it uses a plugin architecture, making it much easier to add new capabilities. A new release with this new architecture (and exciting new capabilities) should be available by the end of the month.

2 1