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'''I wonder if it is possible to modify the nmr-relax programme so that I can do model-free analysis with data from only one field strength? Alternatively, do you know of any programme (that can be installed on Windows) that can do such analysis?'''
The subject of single field strength data has been discussed numerous times on this mailing list. <br> It is recommended to read previous responses to questions relating to single field strength data, and look the other messages in those threads. <br> You will find these discussions quite informative and highly detailed:
#- Martin Ballaschk: http://thread.gmane.org/gmane.science.nmr.relax.user/1409/focus=1438
#- Hongyan Li: http://thread.gmane.org/gmane.science.nmr.relax.devel/694/focus=701
These will have lots of additional information. This is just a selection of possibly the most useful messages. You will soon see that this is a complicated topic. Note that relax is capable of performing 100% of the functionality of:
* Modelfree4 (with or without the Fast-Modelfree GUI interface)
* f) Check for convergence (identical chi-squared values to a previous iteration, and not necessarily the last one). If no, then go back to b) and repeat. Note that the chi-squared value can go up significantly between iterations, but this is because the model is simplifying itself at a much faster rate by loosing parameters - it's Occam's razor at work. Again see the [d'Auvergne and Gooley, 2008b] paper for figures demonstrating this. The concept as to what is happening during this combined model-free optimisation and model selection algorithm is described in the [d'Auvergne and Gooley, 2007] paper. It can take up to 20 iterations or more to reach convergence, depending upon the quality of the relaxation data and the 3D structure or the system in study.
* g) Once steps a-f have been completed for all global models (characterised by the spheroid, prolate spheroid, oblate spheroid, andellipsoid diffusion tensors), then model selection between thedifferent global models needs to be performed.
* h) Monte Carlo simulations for error analysis must be performed at the end.