Index: /issm/trunk-jpl/src/c/analyses/AdjointHorizAnalysis.cpp
===================================================================
--- /issm/trunk-jpl/src/c/analyses/AdjointHorizAnalysis.cpp	(revision 26037)
+++ /issm/trunk-jpl/src/c/analyses/AdjointHorizAnalysis.cpp	(revision 26038)
@@ -2032,10 +2032,27 @@
 
 		/*Build gradient vector (actually -dJ/dD): */
-		for(int i=0;i<numvertices;i++){
-			ge[i]+=-2.*drag*dalpha2dk*((lambda*vx+mu*vy))*Jdet*gauss->weight*basis[i];
-			_assert_(!xIsNan<IssmDouble>(ge[i]));
-		}
-	}
-	gradient->SetValues(numvertices,vertexpidlist,ge,ADD_VAL);
+		if(control_interp==P1Enum){
+			for(int i=0;i<numvertices;i++){
+				ge[i]+=-2.*drag*dalpha2dk*((lambda*vx+mu*vy))*Jdet*gauss->weight*basis[i];
+				_assert_(!xIsNan<IssmDouble>(ge[i]));
+			}
+		}
+		else if(control_interp==P0Enum){
+			ge[0]+=-2.*drag*dalpha2dk*((lambda*vx+mu*vy))*Jdet*gauss->weight;
+			_assert_(!xIsNan<IssmDouble>(ge[0]));
+		}
+		else{
+			_error_("not supported");
+		}
+	}
+	if(control_interp==P1Enum){
+		gradient->SetValues(numvertices,vertexpidlist,ge,ADD_VAL);
+	}
+	else if(control_interp==P0Enum){
+		gradient->SetValue(vertexpidlist[0],ge[0],ADD_VAL);
+	}
+	else{
+		_error_("not supported");
+	}
 
 	/*Clean up and return*/