Giorgio Tomasi, Thomas Skov and Frans van den Berg
Introduction
Many analytical signals based on time-trajectories show artifacts appear as shifts. Of the many algorithms developed to correct for these artifacts DTW (named Dynamic Multi-way Warping – DMW – to distinguish it form other implementations) and COW are implemented as Matlab code.
Reference
Main reference for alignment:
Correlation Optimized Warping and Dynamic Time Warping as Preprocessing Methods for Chromatographic Data. Tomasi, G., van den Berg, F., Andersson, C., Journal of Chemometrics 18(2004)231-241
Automatic selection of COW parameters by “optim_cow.m”:
Automated Alignment of Chromatographic Data. Skov T, van den Berg F, Tomasi G, Bro R (2006) Automated alignment of chromatographic data, Journal of Chemometrics, 20 (11-12): 484-497
Source
Theory
• Small fix in “optim_cow” to make it backwards compatible with Matlab version 6.5.
• A much faster implementation (also closer to the original paper); new function “cow_apply” to apply an (old) computed warping path to new data; scripts changed to new functionality (061219).
• Rather silly mistake in “coshift” for correction in 2D landscapes fixed (060206); should work now.
• Based on some clever tricks by GT (051001), COW had become a lot faster! Also, a function for finding a good reference from a series of objects has been added (“ref_select.m”; work on this is still in progress). 051003 – small bug-fixes (only active when manual segment indexing is used), added fourth example script to illustrate the potential of manual segment indexing.
• In the new release (050509) some minor adjustments have been made plus a third sample script is added to show how the diagnostics output can be used to corrected a signal (so, correction based on previous alignment operation, e.g. in the case of a multi-channel measurement).
• In the new release (050106) some diagnostic-plotting adjustments have been made, a second sample script is added and – most important – the English spelling has been corrected!
• In the new release (041207) some (minor) errors have been corrected, a simple “linear” shift routine for vectors and matrices is added (and improved a little in December), and we have included a small sample script to illustrate use of the code.
