Index: /issm/trunk-jpl/src/c/analyses/ExtrapolationAnalysis.cpp
===================================================================
--- /issm/trunk-jpl/src/c/analyses/ExtrapolationAnalysis.cpp	(revision 21419)
+++ /issm/trunk-jpl/src/c/analyses/ExtrapolationAnalysis.cpp	(revision 21420)
@@ -128,4 +128,8 @@
 	workelement->GetVerticesCoordinates(&xyz_list);
 
+	/* In 3d we are going to extrude using horizontal diffusion. Since the layers are 3d,
+	 * we change the geometry of the element to make it flat. That way, the diffusion is
+	 * handled along the layers
+	 */
 	if(element->ObjectEnum()==PentaEnum){
 		for(i=0;i<3;i++) xyz_list[3*i+2] = 0.;