Notes for Collection of Sand - essays by Italo Calvino

Collection of Sand is a collection of book reviews, exhibition reviews and travelogues that Italo Calvino wrote in the 70’s and 80’s. The quality varies. The best of them are unsurprisingly ekphrastic essays where Calvino described gardens, historical sites, and paintings in exquisite details. Those where he tried to regurgitate scientific or historical knowledge from academic books are less inspiring. But still, it is the variety of things that Calvino cared to write about that charms.
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Who did the first computer simulation of a biological neuron?

Nobel laureates Alan Hodgkin and Andrew Huxley are sometimes called the fathers of computational neuroscience, because they developed the first mathematical theory to explain how neurons communicate with each other with electrical signals. I read in a textbook that when they published their model in 1952, all the numerical calculations were done manually, because the computer at Cambridge was not working. It was “computational” all right, but it was the labour intensive variety.
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Let's make some spirals

Disk point picking is an elementary problem in geometry. To evenly distribute points on a disk, an intuitive idea is to sample pairs of numbers in polar coordinate (radius and angle) randomly from uniform distributions. After all, “uniformly” is just another word for “evenly”, isn’t it? But it doesn’t work. When the points are sampled this way, the density of the dots fall off linearly with the distance to the origin.
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Gradient descent on a non-Euclidean surface

Is the salesman travelling on foot or on an airplane? This article describes an experiment to develop a version of the elastic net algorithm that works on spherical surfaces. I needed it for a computational neuroscience problem, but for those who are mainly interested in machine learning, it also serves a simple and intuitive demonstration of using gradient descent on non-Euclidian surfaces. The Tensorflow source code is available on GitHub. I also made a youtube video showing the algorithm in action.
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Punning is no fun in Chinese

The Economist is probably not the best place to look for rigorous scholarship on comparative punnology, but a recent article did ask a very good question: Why English is such a great language for puns? I am not sure if the superiority of English in punning is that obvious, but the argument seems to be convincing: For English is unusually good for puns. It has a large vocabulary and a rich stock of homophones from which puns can be made.
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