# Brilliant 10: The Computational Contortionist

Rendering complex objects realistically requires a whole new kind of geometry

Complex Folding Computer scientist Eitan Grinspun studies how long, thin strands, such as spaghetti and undersea data cables, twist and coils John B. Carnett

When Eitan Grinspun’s adviser at the California Institute of Technology asked him to help develop a better way to model how cans bend when crushed, the young mathematician did not think it would be a major project. “He lured me into something that took years and years,” says Grinspun, now at Columbia University. But the journey to model a crushed Coke can ended with an entirely new field of geometry.

Differential geometry can describe how the curves and surfaces of a given object will bend and crease. The problem, Grinspun says, is “that differential geometry is built for smooth surfaces with infinite detail.” Computers can process only a finite amount of detail. For example, to describe a circle, computers must divide that circle into a series of connecting short sides—the greater the number of sides, the smoother the circle. Describing all of the curves and creases in a crushed can accurately takes a huge amount of processing power, so Grinspun—one of only a couple of mathematicians in the field with a background in computer science—set about translating the theorems into a more elegant set of instructions for the computer, allowing existing processors to break the infinite into discrete units far more efficiently.

Grinspun's method works by concentrating on the places where most of the movement will occur—in the case of the Coke can, the areas where it folds as it crumples. “There are a lot of flat regions where not much is happening,” he says. “If a computer spreads its attention equally, it’s not going to the interesting parts, where cracks are forming.”

Once Grinspun and his colleagues established this new approach, which they call discrete differential geometry, the queries from physicists, engineers and animators started arriving. Disney and Weta Digital use his theorems to make fabrics and hair move more convincingly. Physicists at MIT have created origami out of small sheets of plastic and water drops. Engineers can now far more accurately predict how cables will fall to the seafloor. “For me, [this field] is a playground,” he says. “I get to take any interesting physical problem—say, spaghetti movement. Toss it in the air, and it falls on the ground and it twists and coils. Why does it move that way?"

In this video, a team of researchers use Grinspun's flexible strand technology to create capillary-powered origami.

To this gentleman, I read the articles and saw his movies and well YES he is brilliant and FUN to watch. Well I have 20 marbles in my head, and I feel this guy has bunches and bunches, say 100 marbles in his head.

I just wanted to avoid having said extra noodles. It just seems so obvious.

Another thing, he has a genuine nice personality. I really wish he was my neighbor too.
What a nice guy!

This guy may actually be able to mathematically predict one of the greatest wonders of the world - How computer and power cables can become such a jumbled entanglement under/behind a desk when they were neatly draped their during installation. :)

His true genius will be revealed once he publishes his new book, understand woman. Now that is a entanglement all us men wish to understand!

I am pretty confident that as you add to your computer, one of the last things you consider is how the addition of another wire adds to the jumble. You need to get separators and check the lengths of wire to see how it affects the jumble. Maybe Grinspan can help with that!

It should be interesting to see what applications this will produce.

A twisted drip! I bet he writes spaghetti code. >:(

That first picture reminds me of a few lines from my book as a prophet of the Flying Spaghetti Monster - who keeps me awake on many nights telling me the truths of the universe. That bastard just can't shut up.

"And the Flying Spaghetti Monster became flesh and dwelt among us as a total geek."

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