Revise (#9357)

doc/user-guide/computation.rst

@@ -482,7 +482,7 @@ every 2 points along ``x`` dimension,
 
     da.coarsen(time=7, x=2).mean()
 
-:py:meth:`~xarray.DataArray.coarsen` raises an ``ValueError`` if the data
+:py:meth:`~xarray.DataArray.coarsen` raises a ``ValueError`` if the data
 length is not a multiple of the corresponding window size.
 You can choose ``boundary='trim'`` or ``boundary='pad'`` options for trimming
 the excess entries or padding ``nan`` to insufficient entries,