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20031219: udunits: year 0
- Subject: 20031219: udunits: year 0
- Date: Fri, 19 Dec 2003 15:38:25 -0700
Rick,
You are correct. There is no year 0. Year 1 BCE is immediately
followed by year 1 CE.
The UDUNITS package is consistent with this fact. Other packages might
not be.
Regards,
Steve Emmerson
> To: address@hidden
> cc: Rick Grubin <address@hidden>
> From: Rick Grubin <address@hidden>
> Subject: udunits: year 0
> Organization: NCAR/SCD
> Keywords: UDUNITS
>
> Howdy
>
> I'm trying to help an NCL user debug a date/time issue that involves using
> udunits. The user is using Matlab to write a netCDF formatted file, with a
> particular timestamp:
>
> Matlab:
>
> DATENUM Serial date number.
> N = DATENUM(S) converts the string S into a serial date number.
> Date numbers are serial days where 1 corresponds to 1-Jan-0000.
> [...]
> N = DATENUM(Y,M,D) return the serial date numbers for corresponding
> elements of the Y,M,D (year,month,day) arrays.
>
> >> n = datenum('15-Dec-2001')
>
> n =
>
> 731200
>
> >> m = datenum(2001,12,15)
>
> m =
>
> 731200
>
>
> -and-
>
>
> DATEVEC Date components.
> C = DATEVEC(T) separates the components of date strings and date
> numbers into date vectors containing [year month date hour mins secs]
> [...]
> [Y,M,D,H,MI,S] = DATEVEC(T) returns the components of the date
> vector as individual variables.
>
> >> c = datevec(731200)
>
> c =
>
> 2001 12 15 0 0 0
>
> -----------------------
>
> Within NCL, where the version of udunits library in place is v1.12.0, the
> user takes his Matlab-created netCDF file and (in essence) does:
>
> ncl 0> time = 731200
> ncl 1> time@units = "Days since 0-1-1 00:00:00"
> ncl 2> print (ut_calendar(time, 0))
>
> and sees
>
> (0,0) 2002
> (0,1) 12
> (0,2) 15
> (0,3) 0
> (0,4) 0
> (0,5) 0
>
>
> I'm trying to figure out where the extra year that NCL/udunits
> reports comes from. Is it a safe assumption that year "0" (or "0000")
> doesn't exist? My long-time (and perhaps muddled) thinking says there is
> no "year 0."
> Thanks,
> -Rick.
> --
> Rick Grubin Visualization + Enabling Technologies
> Scientific Computing Division National Center for Atmospheric Research
> address@hidden 303.497.1832