diff --git a/examples/polyscope-examples/dgtalFEM-poisson.cpp b/examples/polyscope-examples/dgtalFEM-poisson.cpp
index 2b7ca749af..25de9e00ee 100644
--- a/examples/polyscope-examples/dgtalFEM-poisson.cpp
+++ b/examples/polyscope-examples/dgtalFEM-poisson.cpp
@@ -105,7 +105,7 @@ int main()
   auto params = SH3::defaultParameters() | SHG3::defaultParameters() |  SHG3::parametersGeometryEstimation();
 
   auto h=.7   ; //gridstep
-  params( "polynomial", "0.1*y*y -0.1*x*x - 2.0*z" )( "gridstep", h );
+  params( "polynomial", "0.1*y*y -0.1*x*x - 2.1*z" )( "gridstep", h );
   auto implicit_shape  = SH3::makeImplicitShape3D  ( params );
   auto digitized_shape = SH3::makeDigitizedImplicitShape3D( implicit_shape, params );
   auto K               = SH3::getKSpace( params );
diff --git a/src/DGtal/dec/PolygonalCalculus.h b/src/DGtal/dec/PolygonalCalculus.h
index e6cac56c2b..da1fb8da86 100644
--- a/src/DGtal/dec/PolygonalCalculus.h
+++ b/src/DGtal/dec/PolygonalCalculus.h
@@ -1488,10 +1488,14 @@ namespace DGtal
             auto v      = sharp( j, i );
             auto edge_i = mySurfaceMesh->makeEdge( vertices[ i ],
                                                    vertices[ ( i + 1 ) % nf ] );
-            if ( v != 0.0 )
-              triplets.emplace_back( Triplet(
-              (SparseMatrix::StorageIndex)f + j * mySurfaceMesh->nbFaces(),
-              (SparseMatrix::StorageIndex)edge_i, v ) );
+            if(vertices[i] < vertices[(i + 1) % nf])
+            triplets.emplace_back( Triplet(
+                (SparseMatrix::StorageIndex)3 * f + j,
+                (SparseMatrix::StorageIndex)edge_i, v ) );
+            else
+            triplets.emplace_back( Triplet(
+                (SparseMatrix::StorageIndex)3 * f + j,
+                (SparseMatrix::StorageIndex)edge_i, -v ) );
           }
       }
       mySharp.setFromTriplets( triplets.begin(), triplets.end() );
@@ -1510,17 +1514,22 @@ namespace DGtal
         DenseMatrix flat    = this->flat( f );
         const auto vertices = mySurfaceMesh->incidentVertices( f );
         for ( auto i = 0u; i < nf; ++i )
-          for ( auto j = 0; j < 3; ++j )
-          {
-            auto v      = flat( i, j );
+        for ( auto j = 0; j < 3; ++j )
+        {
             auto edge_i = mySurfaceMesh->makeEdge( vertices[ i ],
-                                                   vertices[ ( i + 1 ) % nf ] );
-            if ( v != 0.0 )
-              triplets.emplace_back( Triplet(
-              (SparseMatrix::StorageIndex)edge_i,
-              (SparseMatrix::StorageIndex)f + j * mySurfaceMesh->nbFaces(),
-              v ) );
-          }
+                vertices[ ( i + 1 ) % nf ] );
+            auto v      = flat( i, j ) / (double) mySurfaceMesh->edgeFaces(edge_i).size();
+            if(vertices[i] < vertices[(i + 1) % nf])
+            triplets.emplace_back( Triplet(
+                (SparseMatrix::StorageIndex)edge_i,
+                (SparseMatrix::StorageIndex)3 * f + j,
+                v ) );
+            else
+            triplets.emplace_back( Triplet(
+                (SparseMatrix::StorageIndex)edge_i,
+                (SparseMatrix::StorageIndex)3 * f + j,
+                -v ) );
+        }
       }
       myFlat.setFromTriplets( triplets.begin(), triplets.end() );
       return myFlat;