NMRPipe Processing Functions
CS: Circular Shift.

CS applies a circular-shift to the points in each vector from the current dimension of the data. The shifted points at one end of the vector are moved to the other end of the vector. In this regard, CS mimics the frequency-domain shift which results from applying a first-order phase correction in the time-domain. A circular shift can be applied in either direction, right or left. For example, if an 8-point data vector consists of the following values:

   1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

   7.0 8.0 1.0 2.0 3.0 4.0 5.0 6.0 

   3.0 4.0 5.0 6.0 7.0 8.0 1.0 2.0

The CS function will only shift by an integer number of points; for shifting data by a fractional number of points, use the FSH function.

OPTIONS

-rs rsVal
Specifies the number of points for the shift. If the number is positive, the data will be shifted to the right. If it is negative, the data will be shifted to the left. This value can also be specified with spectral units (% Hz ppm). In these cases, the amount of shift requested will be rounded to the nearest integer.

-ls lsVal
Specifies the number of points for the shift. If the number is positive, the data will be shifted to the left. If it is negative, the data will be shifted to the right. This value can also be specified with spectral units (% Hz ppm). In these cases, the amount of shift requested will be rounded to the nearest integer.

-sw
If this flag is used with frequency-domain data, the chemical shift calibration information is updated (NDORIG and NDCENTER).

-neg
If this flag is used, the points shifted from one side of the vector will be negated; this corresponds to sign inversion which occurs to aliased (folded) points in the frequency domain from time-domain data with a half-point delay (time domain data which require first-order phase P1 = 180). For example, if an 8-point data vector has the values:

   1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

   -7.0 -8.0 1.0 2.0 3.0 4.0 5.0 6.0

EXAMPLES

CS is commonly used as a convenience to move spectral signals to a more convenient position. For example, in the indirect 1H dimension of an 15N 3D NOE experiment, a sufficiently large but arbitrary circular shift can be applied to move the diagonal so that it is not folded over the edges of the spectrum. Note that when CS is applied, the requested shift is always rounded to an integer number of points; for shifting data by a fractional number of points, use the FSH function.

xyz2pipe -in fid/test%03d.fid -x -verb \
| nmrPipe  -fn SOL                                    \
| nmrPipe  -fn SP -off 0.5 -end 0.98 -pow 2 -c 0.5    \
| nmrPipe  -fn ZF -auto                               \
| nmrPipe  -fn FT                                     \
| nmrPipe  -fn PS -p0 167  -p1 0.0 -di                \
| nmrPipe  -fn EXT -x1 10.5ppm -xn 6ppm -sw           \
| nmrPipe  -fn TP                                     \
| nmrPipe  -fn SP -off 0.5 -end 0.98 -pow 1 -c 1.0    \
| nmrPipe  -fn ZF -auto                               \
| nmrPipe  -fn FT                                     \
| nmrPipe  -fn PS -p0 -135 -p1 360 -di                \
| nmrPipe  -fn POLY -auto -ord 0                      \
| nmrPipe  -fn CS -rs 1ppm -sw                        \
| nmrPipe  -fn TP                                     \
| nmrPipe  -fn POLY -auto                             \
| pipe2xyz -out ft/test%03d.ft3 -y

SEE ALSO

Shifting functions LS (left-shift, integer number of points) RS (right-shift, integer number of points) FSH (circular-shift, fractional number of points) and phase-correction function PS which can be used to apply the equivalent of a circular shift in one domain by applying a first order phase correction in the other domain.

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last updated: Apr 20, 2011 / big frank

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