W B Langdon Non-GP 2009 Abstracts

W.B.Langdon . 20 February 2018 2009 papers , full list

Probes containing runs of guanine provide insights into the biophysics and bioinformatics of Affymetrix GeneChips,

W. B. Langdon and Graham J. G. Upton and Andrew P. Harrison, Briefings in Bioinformatics, 2009 10(3):259-277. doi:10.1093/bib/bbp018


The reliable interpretation of Affymetrix GeneChip data is a multi-faceted problem. The interplay between biophysics, bioinformatics and mining of GeneChip surveys is leading to new insights into how best to analyse the data. Many of the molecular processes occurring on the surfaces of GeneChips result from the high surface density of probes. Interactions between neighbouring adjacent probes affect their rate and strength of hybridization to targets. Competing targets may hybridize to the same probe, and targets may partially bind to more than one probe. The formation of these partial hybrids results in a number of probes not reaching thermodynamic equilibrium during hybridization. Moreover, some targets fold up, or cross-hybridize to other targets. Furthermore, probes may fold and can undergo chemical saturation. There are also sequence-dependent differences in the rates of target desorption during the washing stage. Improvements in the mappings between probe sequence and biological databases are leading to more accurate gene expression profiles. Moreover, algorithms that combine the intensities of multiple probes into single measures of expression are increasingly dependent upon models of the hybridization processes occurring on GeneChips. The large repositories of GeneChip data can be searched for systematic effects across many experiments. This data mining has led to the discovery of a family of thousands of probes, which show correlated expression across thousands of GeneChip experiments. These probes contain runs of guanines, suggesting that G-quadruplexes are able to form on GeneChips. We discuss the impact of these structures on the interpretation of data from GeneChip experiments.

A Fast High Quality Pseudo Random Number Generator for nVidia CUDA

W. B. Langdon. Presented at CIGPU 2009, pages 2511-2513. PDF. DOI.


Previously either due to hardware GPU limits or older versions of software, careful implementation of PRNGs was required to make good use of the limited numerical precision available on graphics cards. Newer nVidia G80 and Tesla hardware support double precision. This is available to high level programmers via CUDA. This allows a much simpler C++ implementation Park-Miller random numbers, which provides a four fold speed up compared to an earlier GPU implementation. CUDA C code is available via ftp.

Evo_Indent Interactive Evolution of GNU indent Options

W. B. Langdon Late Breaking paper at GECCO 2009 PDF. DOI


Evo_Indent is a PHP web server based user driven genetic algorithm which finds good C code layouts generated by GNU indent. Either the refactored source can be used or the user's preferred indent command options can be saved and re-used to pretty print other program text files.