The story behind a photo
Editor’s Note: Looking through some old photo files in the University Communications
office, we found the picture at left of Rich Cebula from his IWU student days. Curious,
we wrote him asking to explain what device was shown in the background of the photo.
The image sparked some fascinating memories for Cebula about working on early computers
at the University. He wrote back the following:
I'd completely forgotten having my photo taken. In this photo, probably taken in 1976
or 1977, I am sitting front of a analog computer, a device which really fascinated
me. You might ask what is an analog computer. To that end, I've gone to the Internet
for some material:
"Analog computers are based on principles completely different from digital computers.
Problem variables are represented by electrical voltages which can vary continuously
within a certain range, usually -10 to +10 volts for a transistor-based machine. Electronic
circuit modules allow the variables to be added, integrated (with respect to time)
and multiplied by a constant. This makes it is possible to solve a system of ordinary
linear differential equations by properly combining a number of adders, integrators,
amplifiers and potentiometers using flexible chords and a patch panel."
"An analog computer...is designed to process data in which the variable quantities
vary continuously. It translates the relationships between the variables of a problem
into analogous relationships between electrical quantities, such as current and voltage,
and solves the original problem by solving the equivalent problem, or analog, that
is set up in its electrical circuits. Because of this feature, analog computers were
especially useful in the simulation and evaluation of dynamic situations, such as
the flight of a space capsule or the changing weather patterns over a certain area."
Back in 1970s at IWU, analog computers were a great teaching device that allowed students
to solve differential equations relating to physical processes — for example forced,
damped, harmonic motion. The output of the computer (solution to a problem) was graphically
presented; note the pen plotter in the photo. We programmed by the computer by setting
up the electrical equivalent of the problem to be solved, and then could vary the
parameters associated with the problem (e.g., the forcing function, damping constants,
etc.) and immediately see the impact of these variations on the solution to the problem
at hand. IWU's analog computer was a wonderful visualization tool, especially for
those of us who, like me, were mathematically challenged! -— Rich Cebula
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