# Jonathan Leto: December 2008 Archives

## CyborgCamp: Notes from Evolution of the Language of Technology

Bill DeRouchey (@billder) was the opening presentation at CyborgCamp and was wonderfully entertaining and informative. Here are some quick notes I took:

• How did the "Play/Pause" button become univerally understood?
• Typewriters choose the winning "letter symbols"
• Symbols evolve.
• Are we losing some types/modes of literacy? Is that such a bad thing?
• @ - commerce symbol "each at", then location, then identity
• # - means a group on twitter "context, topic"
• Mouse pointer ~1984
• Future directions in the evolution of tech languages?
• Splintered groups of tech languages
• Emotional bandwidth
• Gatekeepers of knowledge, screening out less knowledgeable people

## 5 Minute Math Lesson: What is a metric tensor and what is it good for?

A metric tensor is used to measure distances based on a given coordinate system. In terms of the Jacobian, the metric tensor can be found from where is the transpose of the Jacobian. Since is a symmetric matrix for any matrix , the metric tensor is always symmetric. (In fancy-pants math lingo this is called a symmetric bilinear form.) What is the real-life consequences of this? The distance from to is always the same as the distance from to , no matter what kind of crazy coordinate system you are living in!
If we want to calculate the length of a parameterized curve where is a parameter with respect to some coordinate system, then we can write an infintesmal displacement element as . The length of this displacement is and the length of the curve from to is .
So we need the metric tensor to define distance along a curve when we are in non-cartesian coordinate systems, such as spherical or toroidal. From the metric tensor one can then start to study the "curvature" of a coordinate system. More soon!

### Pages

This page is a archive of recent entries written by Jonathan Leto in December 2008.

Jonathan Leto: November 2008 is the previous archive.

Jonathan Leto: January 2009 is the next archive.

Find recent content on the main index or look in the archives to find all content.

42