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qac_stats - provide statistics that can be used as regression


The QAC_STATS is a series of numbers associated with a file
      QAC_STATS: ngc0001.ccd -4.29944e-05 0.0126181 -0.0720263 0.0892035  75.9081
-0.00437804  1034
that represent the mean, rms, min and max of a set of numbers. Optionally there are 2 or more numbers present: the flux and the signal ratio sratio=(psum+nsum)/(psum-nsum), where the sums are over the positive and negative values, and npts. For sratio=0 (or near 0) there is no signal, it’s mostly noise, whereas for sratio=1 (or near 1) it’s all/mostly signal.

It is used by a number of programs in NEMO, e.g. tabstat(1NEMO) and ccdstat(1NEMO) where the keyword qac=t needs to be used to active this style of output.


Of course all of the interesting science happens near sratio=0 and one will need more sophisticated signal detection schemes, but the sratio is useful for regression.


A table spectrum with some continuum flux:

    nemoinp 1:10000 | tabmath - - ’rang(0.2,1)’ all seed=123 | tabstat - qac=t
    QAC_STATS: TAB 0.204891 1.01051 -4.2138 4.04915  2048.91 0.247613  10000

and a map, with some flux

    ccdgen - noise 0.2,1 size=100,100 seed=123 | ccdstat - qac=t label=CCD
    QAC_STATS: CCD 0.208417 1.00315 -3.6169 4.1858 2084.17  0.255943  10000

See Also

tabstat(1NEMO) , ccdstat(1NEMO) , ccdgen(1NEMO) , tabmath(1NEMO) , nemoinp(1NEMO)


Peter Teuben

Update History

4-dec-2021   document created     PJT
19-jun-2023    fix CCD example        PJT

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