NMRPipe Processing Functions
FT: Complex Fourier Transform.

Flag Argument Default Description
 -auto Choose Mode Automatically.
 -real Transform of Real-Only Data.
 -inv Perform Inverse Transform.
 -alt Use Sign Alternation.
 -neg Negate Imaginaries.
 -null No FT Processing, Adjust Header Only.
 -bruk Redfield Sequential Data (Same as: FT -alt -real).
 -dmx Force Digital Oversample Adjustment ON (Bruker DMX, JEOL Delta).
 -nodmx Force Digital Oversample Adjustment OFF.

FT applies a complex Fourier transform (FT) to produce a complex result. There is no requirement for a power-of-two data size, but processing times will likely be slower for non-power-of-two cases. FT options include selection of forward or inverse transform, negation of imaginaries before transformation, and sign-alternation (negation of alternating points) of the data before transformation. An option to apply a complex FT to a real data sequence is also provided for TPPI-mode data. FT options can also be selected automatically from the header, provided that the acquisition mode information was recorded appropriately during conversion.

According to the usual convention, the forward FT arranges a frequency-domain result such that zero frequency is in the center of the spectrum, specifically, at point 1 + N/2 of 1 to N (e.g. point 513 of 1 to 1024). The forward/inverse Fourier transform pair are scaled in such a way that a forward FT followed by an inverse FT will recover the original intensities.

If a given dimension of a spectrum is reversed, then that dimension should be processed using FT -neg ... note that simply reversing the order of data points via nmrPipe -fn REV alone is not correct. If a given dimension of a spectrum has its first and second halves rotated, then that dimension should be processed using FT -alt. In some cases, both -neg and -alt might both be needed for a given dimension.

The auto-mode option -auto is intended primarily for use in special-purpose applications which automate an entire conversion and processing scheme, or for use in pulse-sequence specific examples. Its use for routine processing is not recommended.


The following are basic outlines of common 2D Fourier transform schemes (complete schemes would also include a window function and zero fill for each dimension):