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tabclip - clip a table
tabclip [parameter=value]
tabclip
removes points from a table based on some "smoothness" criteria. Examples
are when there is a jump larger than a critical amount it can be flagged.
Or when the derivative exceeds a certain amount.
Fitting programs, such
tabnllsqfit(1NEMO)
can also be used to remove points that are not close
to a global model.
The following parameters are recognized
in order; they may be given in any order if the keyword is also given. Use
--help to confirm this man page is up to date.
- in=
- Input file name (an ascii
table).
No default
- out=
- Output table
No default
- xcol=
- x coordinate column
[1]
- ycol=
- y coordinate column
[2]
- clip=
- Clipping if abs(derivative) exceeds this value
- eta=
- Clipping
if the value predicted from a 2nd order polynomial value exceeds the Y
value by more than eta. This mode only works well on smooth data, and should
not be applied to noisy data.
Default: not used.
- logic=and|or
- When a left and right side criteria is applied,
this determines the outcome of the clipping. and requires both to be satisfied,
or requires only one. deprecated
[Default: and].
- nmax=
- Hardcoded allocation space, if needed for piped data.
- comment=t|f
- Keep the clipped points as comments in the output file?
By default they are shown as comments. [t]
The value of clip= is
very important. It should be a few times the sigma in the signal variation
(see e.g. tabtrend(1NEMO)
how to obtain this). Here we mean the signal to
be all but the outliers. When this clip value is too high, you will see
the reported sigma increase as outliers are now taken into the signal.
If too low, sigma will also decrease and too much signal is removed. Recall
the sigma in the differences is sqrt(2)
the value of the original sigma.
Thus there is an optimal value for clip=.
tabclip cliptest.tab . clip=1
### nemo Debug[0]: X: min/max = 0 99 ### nemo Debug[0]: Y: min/max =
-11.0065 11.8708 ### nemo Debug[0]: Min/Max for deriv = -0.353729 0.279371 (with
clip=1) ### nemo Debug[0]: Sigma = 0.136388 clip/sigma=7.33205 ### nemo
Debug[0]: Wrote 89/100 points
tabmath(1NEMO)
, tabnllsqfit(1NEMO)
Peter Teuben
23-Nov-02 V0.1 Created PJT
27-nov-02 V0.3 added eta= PJT
28-dec-2025 V0.5 ANSI C clean up, use clip= PJT
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