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> address@hidden = "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
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