Hi Troels, Do you have a literature reference where this is inverted? Have a look at Art Palmer's 2001 review: - Palmer, A. G. III, Kroenke, C. D. and Loria J. P. (2001) Nuclear Magnetic Resonance Methods for Quantifying Microsecond-to-Millisecond Motions in Biological Macromolecules. Methods Enzymol., 339, 204-238. (http://dx.doi.org/10.1016/S0076-6879(01)39315-1). Specifically at the top of page 216 where you can see: tan(theta) = omega1 / Omega. Therefore: theta = arctan(omega1 / Omega). So it should be correct in relax using the atan2() function. Or am I missing something? Regards, Edward On 25 July 2014 19:45, Troels Emtekær Linnet <tlinnet@xxxxxxxxxxxxx> wrote:
Hi Edward. I was stumpling over the expression theta = atan2(omega1, Delta_omega) in: specific_analyses/relax_disp/data.py in return_offset_data(). atan2 requires: math.atan2(y, x) Return atan(y / x), in radians. The result is between -pi and pi. The vector in the plane from the origin to point (x, y) makes this angle with the positive X axis. The point of atan2() is that the signs of both inputs are known to it, so it can compute the correct quadrant for the angle. For example, atan(1) and atan2(1, 1) are both pi/4, but atan2(-1, -1) is -3*pi/4. But what is y, and x? If I look at my own figure at: http://wiki.nmr-relax.com/images/1/12/Fig1_Palmer_Massi_2006.png I would say that y is Delta_omega, and x is omega1. Have I done this wrong earlier? Best Troels _______________________________________________ relax (http://www.nmr-relax.com) This is the relax-devel mailing list relax-devel@xxxxxxx To unsubscribe from this list, get a password reminder, or change your subscription options, visit the list information page at https://mail.gna.org/listinfo/relax-devel