Monday, August 22, 2011

Plotting a Complex Exponential

We rewrote one of the MIT OCW 18.03 ODE Mathlets in Python. This mathlet was for plotting complex exponentials.
```from pylab import *
from matplotlib.widgets import Slider

ax = subplot(121)
l1, = plot(None,None, lw=2, color='red')
axis([-1, 1, -8, 8])
title ('\$(a + bi)t\$', color='blue')
grid()

ax = subplot(122)
l2, = plot(None,None, lw=2, color='red')
axis([-3, 3, -3, 3])
title ('\$e^{(a + bi)t}\$', color='blue')
grid()

axcolor = 'lightgoldenrodyellow'
axa = axes([0.15, 0.1, 0.65, 0.03], axisbg=axcolor)
axb  = axes([0.15, 0.15, 0.65, 0.03], axisbg=axcolor)

slidera = Slider(axa, 'a', -1.0, 1.0, valinit=0)
sliderb = Slider(axb, 'b', -8.0, 8.0, valinit=0)

def update(val):
a = slidera.val
b = sliderb.val
t = arange(-1.0, 1.0, 0.001)
l1.set_xdata(t)
l1.set_ydata((b/a)*t)

t = arange(-3.0, 3.0, 0.001)
l2.set_xdata(exp(a*t)*cos(b*t))
l2.set_ydata(exp(a*t)*sin(b*t))
draw()

slidera.on_changed(update)
sliderb.on_changed(update)

show()
```

Wednesday, August 3, 2011

VPython Spring System

VPython is a great package for 3D modeling and visualization. To setup on Ubuntu "sudo apt-get install python-visual". It supports physical constraints, modeling out-of-the-box, so setting up planets, orbits, or a spring system like the one below is very easy. All example codes in VPython package can be found here. Script crystal.py was particularly interesting (output seen below). We used recordmydesktop to record the output, and ffmpeg to convert the ogv output to gif.