Raise an exception if number of elements changes.
Raise an exception if number of elements changes.

Carralex/landlab,csherwood-usgs/landlab,SiccarPoint/landlab,RondaStrauch/landlab,RondaStrauch/landlab,ManuSchmi88/landlab,csherwood-usgs/landlab,ManuSchmi88/landlab,cmshobe/landlab,landlab/landlab,cmshobe/landlab,landlab/landlab,amandersillinois/landlab,landlab/landlab,Carralex/landlab,cmshobe/landlab,RondaStrauch/landlab,SiccarPoint/landlab,amandersillinois/landlab,Carralex/landlab,ManuSchmi88/landlab,laijingtao/landlab,laijingtao/landlab