CDF_EPOCH_COMPARE
-----------------

The CDF_EPOCH_COMPARE function compares a source epoch, either a scalar or an
array of epoch values (date and time), against a base epoch, also a scalar
or an array of values. The epoch can be one of the
CDF formats, CDF_EPOCH, CDF_EPOCH16 and CDF_TIME_TT2000. While data of type
CDF_EPOCH and CDF_EPOCH16 can be compared with each other, data in
CDF_TIME_TT2000 can only be compared with the data of same type.
If the base epoch is a scalar, it is used to compare with all values in the
first epoch. If the base epoch is an array, same element in the source and
base epoch array is compared. If a third argument, endepoch, is provided,
the baseepoch and endepoch are used as the starting and ending epoch that the
source epoch will be checked against. 

Calling the function with two arguments: It returns a scalar value or an
array values of integer of 1, 0, or -1, depending on the source epoch.
If the value of the first epoch is greater (later date and time) than the
base epoch, 1 is set.  If the value of the first epoch is the same as
the base epoch, 0 is set.  If the value of the first epoch is 
less (earlier date and time) than the base epoch, -1 is set.

Returns: A scalar or array of integers of 
   1 :  if epoch1 > baseepoch
   0 :  if epoch1 = baseepoch
  -1 :  if epoch1 < baseepoch

Calling the function with three arguments: It returns a scalar value or an
array values of integer of 1 or 0.

If the value of the source epoch falls within the starting and ending epoch
1 is set. Otherwise, 0 is set.

Returns: A scalar or array of integers of
   1 :  if baseepoch <= epoch1 <= endepoch
   0 :  otherwise

Syntax 
   Result = CDF_EPOCH_COMPARE(epoch, baseepoch [,endepoch]) 

Arguments 
   epoch    A single or an array of epoch value(s) returned from call to 
            CDF_EPOCH,/compute, CDF_EPOCH16,/compute for CDF_EPOCH or 
            CDF_EPOCH16 data type, or CDF_TT2000,/compute for CDF_TIME_TT2000 
            data type, CDF_VARGET, or CDF_VARGET1.

   baseepoch   A single or an array of epoch value(s) returned from call to
            CDF_EPOCH,/compute, CDF_EPOCH16,/compute for CDF_EPOCH or 
            CDF_EPOCH16 data type, or CDF_TT2000,/compute for CDF_TIME_TT2000
            data type, CDF_VARGET, or CDF_VARGET1.

   endepoch   A single or an array of epoch value(s) returned from call to
            CDF_EPOCH,/compute, CDF_EPOCH16,/compute for CDF_EPOCH or
            CDF_EPOCH16 data type, or CDF_TT2000,/compute for CDF_TIME_TT2000
            data type, CDF_VARGET, or CDF_VARGET1. This field has to be 
            of the same data type and dimensionality as baseepoch.


Keywords 
   None

Examples 
   ; For CDF_EPOCH data type
   cdf_varget, id, "Epoch", ep, rec_count=1000,/zvariable
   cdf_epoch, base, 2005,6,1,10,18,17,2,/compute
   ret= cdf_epoch_compare(ep,base)
   help, ret
   ; For CDF_TIME_TT2000 data type
   cdf_varget, id2, "Epoch", ep2, rec_count=1000,/zvariable
   cdf_tt2000, base2, 2005,6,1,10,18,17,2,3,4,/compute
   ret2= cdf_epoch_compare(ep2,base2)
   help, ret2
   ; For CDF_EPOCH data type
   cdf_varget, id3, "Epoch", ep3, rec_count=1000,/zvariable
   cdf_epoch, starting, 2005,6,1,10,18,17,2,/compute
   cdf_epoch, ending, 2005,6,10,10,18,17,2,/compute
   ret3= cdf_epoch_compare(ep3,starting,ending)
   help, ret3

Version History 
  Introduced:  CDF V3.4.0