Anyone who has ever dealt with the statistical analysis of compositional data must have stumbled across John Aitchison’s (1926-2016) log-ratio transformation. The Scottish statistician spent much of his career on the statistics of such data, wrote the famous book “The Statistical Analysis of Compositional Data” (Aitchison, 1986, 2003) and multiple papers on the same topic, with associated MATLAB 5 software package CODA available from the author at the time of publication, updated versions now available for download at CoDAWeb. Aitchison’s log-ratio transformation overcomes the close-sum problem of closed data, i.e. data expressed as proportions and adding up to a fixed total such as 100 percent. The close-sum problem causes spurious negative correlations between pairs of variables that are avoided by logarithmizing ratios of the variables. Here is a simple MATLAB example illustrating the effect of Aitchison’s log-ratio transformation on compositional data. Continue reading “MATLAB Example to Illustrate John Aitchison’s Log-Ratio Transformation”
The spring courses on MATLAB Recipes for Earth Sciences in Potsdam will be held on 18–22 Februar 2019 (in English language) and 4–8 March 2019 (in German language). Continue reading “46th and 47th Shortcourse on MRES in Potsdam”
Sediment data is typically display in diagrams with two axes, a core depth axis and an age axis. Here is a MATLAB script to convert depths into ages and display a sediment parameter in a diagram with both age and depth axis. Continue reading “Displaying Sediment Records with both Age and Depth Axis with MATLAB”
On September 28, 2018, the University of Potsdam will once again open its lecture halls for 8–10 year old children in order to inspire them for the world of science. During the event I will teach a lecture on “Knochenjob in Ostafrika – Unterwegs auf den Spuren der Menschheitsentwicklung” during the Children’s University Potsdam.
On 12 September at 11 a.m. I will teach a including the newest results from our Chew Bahir Project during Potsdam Summer School 2018. on “The skin of our planet – the Earth surface system”. In partnership with GeoX and the City of Potsdam, this summer school is organized by AWI, GFZ, IASS, PIK and U Potsdam. Continue reading “Lecture on Tectonics, Climate and Human Evolution”
Convolving distributions corresponds to adding independent random variables. MATLAB is a great tool to demonstrate the convolution of distributions. Continue reading “Convolution of Distributions”