[phenixbb] question about FFT map coefficients

Nathaniel Echols nechols at lbl.gov
Thu Mar 28 15:42:31 PDT 2013

On Thu, Mar 28, 2013 at 3:28 PM, Michael Thompson <miket at chem.ucla.edu> wrote:
> I have an mtz file with map coefficients that are essentially Fo-Fo for two data sets. I would like to generate a map using these coefficients, but because the subtraction of Fs has already been done, there are some values of FP that are negative. Is "FFT map coefficients" able to handle negative values for FP?

My guess would be that the answer is yes, because internally the
amplitudes and phases for map calculation are combined to form a
single array of complex numbers, and this effectively converts the
amplitudes to be all-positive.  Also, if this were not the case, the
isomorphous or anomalous difference maps would never work.  But I
haven't actually tried what you're wanting to do with real data - if
the result isn't what you expect, let us know.


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