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Up: PLT Command Summary
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STatistics [fgroup]
where [fgroup] is the default group for fitting. This
command causes a short table to be printed on your terminal that
displays some basic statistical properties about that group of data.
The first line tells you which group is fitted and over what range.
Next the unweighted average, variance, and 3rd moment are displayed.
For the unweighted data, the column labeled SUMW contains the total
number of points used in the calculation, for weighted data, SUMW
is the sum of the weights. YMIN and YMAX are the minimum and
maximum data values in the range. If the plot group has errors
associated with it, then weighted values of the average, variance,
and 3rd moment will be displayed. The next row contains WCHI and
WRED which are the c2 and reduced c2. The W is appended
to remind you that the actual errors on the data were used. The line
labeled Sum of Y*XDEL contains the sum of the y values times the
Dx values, where Dx
is given by the x-error bars. This
is a rectangle rule integral of the data. The last line gives the
(unweighted) linear correlation coefficient of the y vs. x data.
For maximum accuracy, this routine makes two passes through the data,
once to calculate the average, and the second time to calculate moments
based on the difference between the data and the average.
If you don't understand the difference between the unweighted and
weighted values then you should use unweighted quantities.
Example:
PLT> STat
Group 2, from 430.0 , to 540.0
YBAR YVAR Y3M SUMW YMIN YMAX
UNWTD 0.5915 0.1341 -8.3771E-03 23.00 2.2100E-02 1.096
WTD 7.8728E-02 2.0009E-02 1.2435E-02 4.9056E+05
WCHI= 9.389E+03, WRED= 426.768
Sum of Y*XDEL= 0.883411
Correlation coeff.= -0.853596
Web Page Maintained by: Dr. Lawrence E. Brown elwin@redshift.gsfc.nasa.gov
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