where X and Y are the discrete Fourier transforms of
x and y and the Y* denotes complex conjugation. The
cross-correlations are computed by fast Fourier transformation
of the two data sets zero padded to 4096
points, multiplication of one transform by the complex conjugate of the other, and inverse transformation of
the resulting product. A graphical output of the crosscorrelation
of the two “spectra,” Figure 2b and c, is
shown in Figure 2d. The final score attributed to each
candidate peptide sequence is the value of the function
when 7 = 0 minus the mean of the cross-correlation
function over the range -75 < 7 < 75 [30]. The scores
are normalized to 1.0 and termed C