Dear Edward, Sorry for the confusion. I tried to compare the results obtained from Modelfree4 and relax using the isotropic model (since I cannot get Modelfree4 works on axial symetric model at moment). 't-rex-sim.agr' corresponds to results from Modelfree4 and 't-rex-relax.agr' corresponds to the results from relax. Using Modelfree4 there are more residues fitted to M5 where using relax, more residues were fitted by M2 and M4, I supposed that is due to different criteria on model selections. However, one thing I don't understand is that te extracted from M2 and M4 should be on a scale of several hundreds ps (fast) instead of several thousands ps (slow). In this regards, Modelfree4 is more resonable and there seems some problem in terms of model elimination and model selection for the Relax. Best wishes, Hongyan Quoting Edward d'Auvergne <edward.dauvergne@xxxxxxxxx>:
Hi, Sorry, I'm not exactly sure what the graphs correspond to. Is 't-rex-sim.agr' Modelfree4 using the prolate (or oblate) spheroid (this is axially symmetric anisotropic Brownian rotational diffusion)? And is 't-rex-relax.agr' the results from relax using the spheroid tensor? Have you used constraints on Da in relax to isolate the oblate and prolate spheroids? Also how many iterations of the model-free optimisation; model elimination; model selection; and global minimisation (the optimisation of the model-free parameters of all spin systems together with the diffusion parameters) have you used? What is the input data and do you have data at more that one field strength? I'll try to answer some of your questions, but without more information these may not be the answers you are after. The first thing which is a little worrying is that in 't-rex-sim.agr' there are many ts values between 6 to 8 nanoseconds. Unless you are working with an unfolded protein or a system that is far from globular, this is a very strong indication that the diffusion tensor is significantly underestimated. How did you determine the initial diffusion tensor in the analyses? Did you use the full_analysis.py script when using relax (which requires data at minimally 2 field strengths)? The errors on the Modelfree ts results are also worrying. This, to me, looks like that there has been failures in the MC simulations causing very similar errors on all the high ts values. Did you use an upper limit of 10 ns in Modelfree? Another worry is that you obtained similar results from relax using the spherical and spheroidal diffusion! How many iterations of model-free analysis did you use? And how did you determine the initial diffusion tensor? As for the te values in the nanosecond range, this is perfectly normal. This is modelling slow internal motions. Model m5 was designed for this purpose, but if the fast internal motion is close to insignificant due to experimental noise, then model m2 is perfectly capable in modelling the slow motion. Also if you set the range of the y-axis in all the correlation time graphs from 0 to 10 ns, then you can see that the results from Modelfree4 are more worrying. For the correlation time results, it is better to make two graphs - one for fast motions up to 200 or so picoseconds and one for slow motions from 200 ps up. Don't forget that what you are doing is modelling. The models don't care what the underlying true dynamics are - they will model that motion as best as they can. So classifying the dynamics based on which model is selected is at best distracting or at worst misleading. It's the results that matter, not the model. I hope this answers some of your questions. Regards, Edward