Fix start time in replicte_cycle for sea-ice data

This merge fixes the starting time of the replicate_cycle function
used to repeat sea-ice climatology data sets.  The start time was
not correct if the comparison data set did not start at the same
time as the first cycle of the repeated data set.

Author: xylar

mpas_analysis/sea_ice/timeseries.py

@@ -306,12 +306,14 @@ def replicate_cycle(ds, ds_toreplicate):
     dsshift = ds_toreplicate.copy()
     shiftT = ((dsshift.Time.max() - dsshift.Time.min()) +
               (dsshift.Time.isel(Time=1) - dsshift.Time.isel(Time=0)))
-    nT = np.ceil((ds.Time.max() - ds.Time.min())/shiftT)
+    startIndex = int(np.floor((ds.Time.min()-ds_toreplicate.Time.min())/shiftT))
+    endIndex = int(np.ceil((ds.Time.max()-ds_toreplicate.Time.min())/shiftT))
+    dsshift['Time'] = dsshift['Time'] + startIndex*shiftT
 
     # replicate cycle:
-    for i in np.arange(nT):
+    for cycleIndex in range(startIndex, endIndex):
         dsnew = ds_toreplicate.copy()
-        dsnew['Time'] = dsnew.Time + (i+1)*shiftT
+        dsnew['Time'] = dsnew['Time'] + (cycleIndex+1)*shiftT
         dsshift = xr.concat([dsshift, dsnew], dim='Time')
     # constrict replicated ds_short to same time dimension as ds_long:
     dsshift = dsshift.sel(Time=ds.Time.values, method='nearest')