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Displaying posts with tag: math (reset)
Running Standard Deviation in MySQL

Calculating the standard deviation in MySQL is a no-brainer by using the build-in aggregate function STDDEV(). If you don't need the original data and only want to save aggregated values in your database, the whole matter is getting more complicated - but is worth from a space and performance point of view.

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MySQL Infusion UDF for statistical analysis

Since I use MySQL for the statistical analysis on a project, I wanted to optimize the database queries and learned a lot about stuff like number theory, set theory and partial sums. I took my MySQL UDF, I've published two years ago, for this purpose and added new functions for a deeper statistical analysis. The project is around for a while, so it's time to share things with the public to start a discussion of how things could be further optimized. The source and a small documentation can be found on Github:

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Calculate date ratios

When I celebrated my birthday, I got the idea that there must theoretically be a date on which two peoples ages are in a certain ratio. The basic idea were born when I thought that there must be a date on which my mother is exactly twice as old as me. Actually, this is the point of time when I'm as old as my mother was, when I were born. That means

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Monotonic functions, SQL and MySQL

In mathematics, a monotonic function (or monotone function) is a function which preserves the given order. [Wikipedia]

To be more precise, a function f is monotonic increasing, if for every x ≤ y it holds that f(x) ≤ f(y). f is said to be strictly monotonic increasing is for every x < y it holds that f(x) < f(y).

So, if we follow values in some order, we say that f is monotonic increasing if f’s value never decreases (it either increases or stays the same), and we say that f is strictly increasing if f’s value is always changes “upwards”.

Monotonic functions play an important role in SQL. To discuss monotonic functions in SQL we must first determine what the order is, and then, what the …

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Four short links: 4 August 2009
  1. NASA Nebula Services/Platform Stack -- The NEBULA platform offers a turnkey Software-as-a-Service experience that can rapidly address the requirements of a large number of projects. However, each component of the NEBULA platform is also available individually; thus, NEBULA can also serve in Platform-as-a-Service or Infrastructure-as-a-Service capacities. Bundles RabbitMQ, Eucalyptus, LUSTRE storage, Fabric deployment, Varnish front-end, MySQL and more. (via Jim Stogdill)
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Tiny Victories, 2006-12-01

It's not often that I get to pull Knuth's The Art of Computer Programming down off the shelf and immediately solve a problem with it. Today, I did.

A big "Thank you!" goes to my parents for giving it to me long ago.

The problem is that for the way almost all computers work, floating-point numbers do not follow the associative property. This results in wrong results and a good bit of hilarity.

Showing entries 1 to 6