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## #245 DC DFT: Current limit of 4 decimal digits of frequencies

closed-fixed
David Benn
5
2011-02-16
2010-12-29
WR
No

Current limit of 4 decimal digits of DC DFT frequencies is much to low:
If one looks at the real long periodic var stars like e.g. alf Ori,
eps Aur, ... the longest detected periods are in the range of 10000d.
The outburst cycle of RNe can and is often even a multiple of this
value.
So the number of significant digits in the DFT frequency output of
0.0001 1/d = 1/10000d is much too less and one cann't use the DFT
for such long periods as the effective period sequence with this
resolution is just:
indefinite=1/0.0000, 10000d=1/0.0001, 5000d=1/0.0002, 3333d=1/0.0003,
2500d=1/0.0004, ... . Smaller frequencies than 0.0001 1/d are always
rounded to 0.0000 1/d, no matter how long they actually are. As the
DFT plot are also just plotted to 0.0001d resolution, they cann't il-
lustrate such long periods at all.

## Discussion

• WR
2010-12-29

• labels: --> User Interface & Usability
• assigned_to: nobody --> david_benn

• WR
2010-12-29

To get an accuratly rounded resolution to 1d at a period of 10000d,
one must give at least 8.5 decial digits (1/10000 - 1/10000.5 ~=
0.000000005)! If one wants to get a rounded period to better than 1d,
one needs even more decimal digits. E.g. for eps Aur the period can
be calculated and rounded to two significant decimal digits which will
require a frequency output of 11 significant digits. As the period is
given to 4 decimal digits in the DFT output, the frequency would re-
quire 13 decimal digits.

• David Benn
2011-01-08

The fix in

currently also applies to frequency values.

• David Benn
2011-02-12

See the new Numeric Precision in version 2.11 (to be released to Citizen Sky in the next few days) preferences which allow you to change the display precision for time, magnitude, and other values.

• David Benn
2011-02-12

• status: open --> open-fixed

• Sara Beck
2011-02-16

• status: open-fixed --> closed-fixed

• Sara Beck
2011-02-16

The Numeric Precision preference option is neat!