[ccp4bb]: inverse maps from fft

[Harry M. Greenblatt]

BS"D Dear All,    I addressed this issue to "management" but got no reply. I wanted to make a map from a published structure, so I downloaded the structure factors and the coordinates, and used the import facility to go from mmcif to mtz.  Then I ran sfall to generate fcalc and phicalc from the coordinates.  Then fft to make a 2fo-fc map.  Looking at the map in PyMOL and then in coot and contouring at 1.5sigma, it was obvious that something had gone wrong.  While looking in coot, and pondering what could be wrong, I was idly scrolling the mouse wheel, which changed the contour.  When I got close to zero, the map suddenly started looking better.  Checking the fft output confirmed my suspicions:  the map, instead of going from -0.6 to +1.6, went from -1.6 to +0.6.  Contouring at -1.5sigma gave what one would expect from a 2fo-fc map.  So I guess the map that was calculated was Fc - 2Fo.       I checked the fft output again and confirmed that FP was F1, whose multiplier, n, was +2.0 and that Fcalc was F2, whose multiplier, m,  was +1.0 and that I had asked for a  nF1 - mF2 map. Perhaps I did something wrong?  Perhaps this is a bug in fft? Thanks, Harry ------------------------------------------------------------------------- Harry M. Greenblatt Staff Scientist Dept of Structural Biology           [EMAIL PROTECTED] Weizmann Institute of Science        Phone:  972-8-934-3625 Rehovot, 76100                       Facsimile:   972-8-934-4159 Israel