NMRPipe Processing Functions
GMB: Another Version of the Gauss Window.

Flag	Argument	Default	Description
`-lb`	`lb`	`0.0`	Exponential Term (APOD Parameter Q1)
`-gb`	`gb`	`0.0`	Gaussian Term. (APOD Parameter Q2)
`-size`	`aSize`	`TSIZE`	Number of Points in Apodize Window.
`-start`	`aStart`	`1`	Start Location for Applying Apodize Window.
`-c`	`fScale`	`1`	Scale Factor for First Point (C1 Parameter).
`-one`			Set window points outside apodize region to 1.
`-hdr`			Use Q1,Q2,C1 Values from Header as Defaults.
`-inv`			Invert Window.

GMB applies a Gauss-like window, inspired by a similar window function found on Bruker spectrometers. It is somewhat similar to the GM function, and like this function, it also applies a combination of an exponential and a Gaussian.

In the following formula for GMB, tSize is th number of time-domain points, which defines the length of the window function; GMB[i] is the window function from i = 0 (first point) to i = tSize - 1 (last point); and sw is the sweep width in Hz.

Given the GMB adjustable parameters lb and gb:

          GMB[i] = exp( -a*t - b*t*t )

where

          t  = i/sw
          aq = tSize/sw
          a  = PI*lb
          b  = -a/(2.0*gb*aq)

In addition to function-specific options, the GMB window function provides the following features common to all NMRPipe window functions:

Optional scaling of the first point of each FID.
Automatic recording of window parameters and first point scaling in the data header during processing.
Automatic adjustment of the default size of the window function to match the valid time-domain size recorded in the header.
Optional extraction and use of window parameters recorded in the header, rather than from the command-line.
An inverse mode, which divides by the window function and first point scale rather than multiplying by them.
Options to adjust the size or starting point of the window function via command-line arguments.

GMB OPTIONS

-lb lbVal
(Q1) Specifies an exponential factor lb, as used in the formula given above. This value is usually specified as a negative number which is about the same size as the natural linewidth in Hz. The default value is 0.0, which means no exponential term will be applied.

-gb gbVal
(Q2) Specifies a Gaussian factor gb, as used in the formula given above. It is usually specified as a positive number which is a fraction of 1.0. The default value is 0.0, which leads to an undefined window function according to the formula; for this reason, the Gaussian term is omitted from the calculation when -gb 0.0 is given.

GENERIC WINDOW OPTIONS

-size aSize
Specifies the number of points in the window function. The default value is the valid time-domain size recorded in the data header.

-start aStart
Specifies the starting point of the window function. The default value is 1, which means the window function starts at the first point of the FID. This option is intended for creation of composite windows by application of different functions to different regions of the FID.

-c fScale
Specifies the scaling applied to the first point of the FID, which influences the zero-order offset in the corresponding spectrum. The default value is 1.0, which means no first point adjustment is applied. A value of 0.5 is usually appropriate in cases where no substantial first-order phase correction will be applied.

-one
This flag influences the values used "outside" the window function, in cases where the window size is smaller than the actual number of data points. By default, data values outside the window region are multiplied by zero when the window is applied. However if the -one flag is used, data values outside the window region will be multiplied by 1.0 when the window is applied. This flag is intended to assist creation of composite windows by application of different functions to different regions of the FID.

-hdr
When this flag is used, default window parameters (Q1 and Q2) will be extracted from the data header, along with the first point scaling (C1). This requires that all of these parameters have already been recorded, for instance during previous processing or format conversion (see EXAMPLES below). Additional command-line can be used to override values restored from the header. The window parameters stored in the data header can be viewed using the showhdr program, for example:

          showhdr -verb test.ft2

-inv
When this flag is used, the inverse (1/window) of the selected window and first point scale will be applied. This option is intended for removing a previously-applied window in inverse processing schemes. This option should generally only be used on window functions which have no values close or equal to zero. In cases where the window does have a zero value, the inverse window is also given as zero.

EXAMPLES

A typical usage of a GM and GMB window:

        nmrPipe -fn GM  -g1  20 -g2 35
        nmrPipe -fn GMB -lb -20 -gb 0.25

HEADER VALUES

GMB and the other nmrPipe window functions use the recorded time-domain size (NDAPOD) to establish their default length.

When the -hdr flag is used, default window parameters are extracted from header values NDAPODCODE, NDAPODQ1, NDAPODQ2, and NDC1.

The header values NDAPODCODE, NDAPODQ1, NDAPODQ2, and NDC1 are updated according to the values applied during processing.

Frank Delaglio, Ph.D.