slight speed up in exterior edges
slight speed up in exterior edges

aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation,JianpingCAI/libigl,JianpingCAI/libigl,JianpingCAI/libigl,JianpingCAI/libigl,JianpingCAI/libigl,JianpingCAI/libigl,aaronzou/Shape-Deformation,aaronzou/Shape-Deformation