Playing Around with Floating Point Numbers with MATLAB

Computers do not work with real numbers, of which there are infinitely many, but with a finite number of floating point numbers. Most real numbers do not exist in computers because they fall between two floating point numbers. Everything we calculate with a computer may therefore have a finite accuracy. Here are some MATLAB examples. Continue reading “Playing Around with Floating Point Numbers with MATLAB”

MATLAB/Simulink Total Academic Headcount License at U Potsdam

Since November 1, 2018, the University of Potsdam offers a university-wide license for MATLAB, Simulink and 50 Toolboxes for all students and employees. This MATLAB Total Academic Headcount License allows all students, faculty and researchers to use the software at their workspace, in the computer pools, in the university’s WiFi network, at home and while traveling.
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MATLAB Example to Illustrate John Aitchison’s Log-Ratio Transformation

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”