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Re: Julian time problem [message #51446]

Sun, 26 November 2006 16:18

badjelly.witch
Messages: 27
Registered: May 2006

Junior Member

Jonathan Dursi wrote:
> In particular, the difference between the two quantities (~4.65e-10) is
> a couple parts in 1e16 of the value (~2.45e6), and you simply can't do
> better than that in the usual IEEE double precision math.

Another issue here, apart from the general imprecision of floating
point math, is that TIMEGEN adds a small offset. From the
documentation:

"A small offset is added to each Julian date to eliminate roundoff
errors when calculating the day fraction from the hour, minute, second.
This offset is given by the larger of EPS and EPS*Julian, where Julian
is the integer portion of the Julian date and EPS is the
double-precision floating-point precision parameter from MACHAR. For
typical Julian dates the offset is approximately 6x10-10 (which
corresponds to 5x10-5 seconds). This offset ensures that when the
Julian date is converted back to the hour, minute, and second, the
hour, minute, and second will have the same integer values."

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[Message index]

		Re: Julian time problem By: badjelly.witch on Sun, 26 November 2006 16:18
		Re: Julian time problem By: Jonathan Dursi on Fri, 24 November 2006 05:30
		Re: Julian time problem By: Paolo Grigis on Fri, 24 November 2006 05:21

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