add fn to gradients
add fn to gradients

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