Computer simulation of physical devices

Computer Simulation Issues

A number of issues arise in simulating even a simple physical device
on a computer. First, I had to write out the equations of motion for
the sculpture. These are the specific instances of Newton's
equation, generally (and nonspecifically) written F = ma. Then, I
wrote a program to compute how these equations evolve in time. I
used a well-known recipe called the fourth-order Runge-Kutta
method.

The program computes the new state of the system every few
milliseconds from the information on its earlier state and the
equations of motion. Ten or twenty milliseconds works well for a
slowly-moving sculpture like the one shown in the movie. The
images on the 3D visualization panel and the phase-space panel are
redrawn as needed. Typically, updating the images twenty times per
second is enough to make the motion appear smooth and
continuous.

That's a lot of computing to be done in every twentieth of a second.
When I started working with computers in 1961, it was impossible for
even the fastest computers on earth. When I got a PDP11 computer
for $75,000 in 1972, it was still impossible. Today, it works
beautifully on a four-year old Dell Inspiron 8500 laptop that was a
free hand-me-down from my daughter.

The simulator is written in the Java computer language. Java is
portable to nearly any modern computer; there are many
accessories available such as 3D graphics (the Java3D package),
media extensions to write JPEG and other image formats and to
make movies (the JMF package); and it's all free.

“I sure wish I had this
book ten years ago.
Some might think that I
don’t need any Java
books, but I need this
one.”

–James Gosling, fellow
and vice president, Sun
Microsystems, Inc.

An introduction to 3D
graphics using Java. A
good way for graphics
beginners to get started
on their home PC.