# Matrix Inversion: Partition Method

### Introduction

Today we will discuss a not-so-famous method of inverting matrices. This method is recursive in the sense that given a method to find inverse of square matrix of order $n$ it can be applied to find the inverse of a matrix of order $(n + 1)$. This method is named Partition Method or the Escalator Method. The idea is to partition a matrix into smaller sub-matrices and then calculate the inverse from the given inverse of one of the smaller sub-matrices.

# Two Problems not from IIT-JEE

After the widely read post Two Problems from IIT-JEE, I am going to discuss two problems which are not from IIT-JEE (as far as I am aware). They are taken from the masterpiece "A Course of Pure Mathematics" by G. H. Hardy. The first one is a tough limit problem (at least I have not been able to find a simpler solution till now) and the second one is an instructive example which deals with the behavior of derivatives for large values of the argument.

# The Riemann Integral: Part 3

### Oscillation of a Function

In a previous post we obtained the Riemann's condition of integrability using the concept of upper and lower Darboux sums. We observed that in order that a function be Riemann integrable on interval $[a, b]$ it was necessary (and sufficient) to make the sum $$U(P, f) - L(P, f) = \sum_{k = 1}^{n}(M_{k} - m_{k})(x_{k} - x_{k - 1})$$ arbitrarily small for some partition $P = \{x_{0}, x_{1}, x_{2}, \ldots, x_{n}\}$ of $[a, b]$.

# The Riemann Integral: Part 2

In the last post we defined the Riemann integral of a function on a closed interval and discussed some of the conditions for the integrability of a function. Here we develop the full machinery of the Riemann integral starting with the basic properties first.