Below you will find my posts on math and programming sorted in reverse chronological order. Generally, I will write about key insights that allowed me to obtain a better understanding of a particular topic, in the hopes that this information is useful to someone. I will also write about topics that I find interesting, but typically only if I have some additional insight that a quick web search or elementary textbook will not reveal. Finally, I enjoy writing posts that introduce someone without the requisite background to key mathematical concepts. I believe that everyone should be allowed a glimpse into the beauty of mathematics - if they have the desire - even though they may not possess the time or inclination to take the mathematical journey themselves.

The Singular Value Decomposition: the Swiss Army knife of data analysis applied to motion capture

The Singular Value Decomposition (SVD) is an incredibly useful tool with a staggering number of applications in seemingly unrelated fields. In this post I want to write about how the SVD is utilized to determine the orientation of a body segment from the skin markers attached to it. It's an interesting application of the SVD because it has straightforward geometrical interpretation.

Intrinsic and extrinsic rotations

Klevis Aliaj
778 words

In this post I want to explore a simple insight about rotating between two orientations. Rotations are notoriously confusing and unintuitive, as evidenced by the fact that Wikipedia lists six different formalisms for representing rotations. Rotations are important to understand, however, because they play an integral role in physics, robotics, biomechanics, 3D animations, and a multitude of other disciplines.

How not to spill your friend's coffee: tensor invariance under coordinate system transformations

Klevis Aliaj
2083 words
When I first began studying continuum mechanics, tensors were a conundrum to me. I understood how to manipulate them algebraically but obtaining an intuitive understanding of them was a more difficult path. The purpose of this post is to simplify tensors for students who may have also run into the same roadblocks as I did. This post assumes familiarity with orthonormal bases, coordinate systems (frames), and measuring the position and orientation of one frame with respect to another.

Measuring position and orientation (with no mathematical notations)

Klevis Aliaj
873 words
In scientific/engineering endeavors, measuring the position and orientation of an object is important because it allows us to quantify movement characteristics. This post aims to provide a simple explanation of the process of measuring the position and orientation of an object in space. The goal is to not use any mathematical notation, although I presume that we all share a common intuitive understanding of the concept of a point and axis in the 3D space we inhabit. My failure to provide even a decent description of how to measure an object's position and orientation highlights the need for the precision introduced via mathematics (or my inability to explain a simple concepts succinctly - I pick the former). For simplicity, I will only consider measuring the position and orientation of rigid bodies, i.e. objects that do not deform.