Category Archives: Algebra

Zeros of random polynomials

Given a polynomial , where the coefficients are random, what can we say about the distribution of the roots (on )? Of course, it would depend on what “random” means. Here, “random” means that the sequence is an i.i.d. sequence … Continue reading

Posted in Algebra, Complex analysis, Potential theory, Probability | Leave a comment

Hopf fibration double covers circle bundle of sphere

Two days ago, I gave a seminar talk on Chern‘s proof of the generalized Gauss-Bonnet theorem. Here I record the answer to a question asked by one of my colleague during the talk. Although not directly related to the proof … Continue reading

Posted in Algebra, Differential geometry, Group theory | Leave a comment

The Cauchy-Schwarz inequality and the Lagrange identity

The classical Lagrange identity is the following: This can be proven by expanding and separating the terms into the cross-terms part and the non cross-terms part. The Lagrange identity implies the Cauchy-Schwarz inequality in . And when , this can … Continue reading

Posted in Algebra, Group theory, Inequalities, Linear Algebra | Leave a comment

27 lines on a smooth cubic surface

Here describes two different proofs of a general smooth cubic surface containing exactly 27 lines. One approach uses blow-ups and the other one uses the Grassmannian. If I have time I will elaborate on the discussion.  

Posted in Algebraic geometry | Leave a comment

Toric perspective 1

This series of posts will be about toric varieties. The author is not sure if there is a part 2, but he still calls this part 1. This post is about computing the dimensions and degrees of popular toric varieties. … Continue reading

Posted in Algebraic geometry, Combinatorics | 2 Comments

A Fibonacci-like sequence

What’s the pattern of the following sequence? Can you guess the next term? The answer is

Posted in Algebra, Combinatorics | Leave a comment

High degree polynomial with few real roots

There are univariate polyomials that the number of non-real roots is significantly larger than that of real roots. The simplest example is where is odd. It has one real root and non-real roots. In this post we show an example … Continue reading

Posted in Algebra, Calculus, Miscellaneous | Leave a comment