# Error in 1D integration

**URL:** <https://community.freefem.org/t/error-in-1d-integration/1554>\
**Category:** General Discussion\
**Created:** [February 24, 2022, 7:03am UTC](https://community.freefem.org/t/error-in-1d-integration/1554 "2022-02-24T07:03:03Z")\
**Posts on this page:** 3\
**Page:** 1

<div class="post-metadata">

**Author:** ![Loic](https://avatars.discourse-cdn.com/v4/letter/l/e9c0ed/32.png) [@Loic](https://community.freefem.org/u/Loic)\
**Post date:** [February 24, 2022, 7:03am UTC](https://community.freefem.org/t/error-in-1d-integration/1554/1 "2022-02-24T07:03:03Z")

</div>

[coarse\_grid.mesh](https://community.freefem.org/uploads/short-url/jzZYIKU9VFbkHBjRli19SCMMRyv.mesh) (266 Bytes)  
[Plane\_1.mesh](https://community.freefem.org/uploads/short-url/1m1iqwdw9uYEXi3kHlFlACiwTSs.mesh) (8.7 KB)

Hello all,

I am running this code:

```auto
verbosity=0;
load "Element_PkEdge";
load "msh3";

meshS TH=readmeshS("coarse_grid.mesh");
fespace Tri(TH,P0); // P0 on coarse mesh
Tri ChiK;

ChiK[][0]=1; // P0 function used to mark the element i
meshS THK=trunc(TH, ChiK>0.1, split=1); // a mesh made of only one triangle;

int[int] lab = labels(THK);
int[int] NewLab = [lab[0],10,lab[1],20,lab[2],30];
THK = change(THK, label=NewLab);
plot(THK, wait=1);
meshS ThK=readmeshS("Plane_1.mesh");

/ ********************************* /
meshL THL= extract(THK); // border mesh
fespace Ehc(THL,P0); // Constant fonction of edge
Ehc ul = region+0.5; // get the label on the each boundary edge
ThK = change(ThK, flabel= dist(THL) < 1e-6 ? ul : 40 ) ;
/ ************************************** /

fespace VHKP0edge(THK,P0edge); //useful to locate the edges of the coarse element
fespace VhK(ThK, [P2, P2]); //FE space to solve the local problem

varf vA([u,v],[uu, vv])=int2d(ThK)((dx(u)*dx(uu)+dy(u)*dy(uu)+dx(v)*dx(vv)+dy(v)*dy(vv))) + on(40,u=0, v=0);
matrix A=vA(VhK,VhK);

func w1 = 1*[1,0];
varf vL([u], [uu,vv]) = int1d(ThK,10,20,30)(u*w1'*[uu,vv]);
matrix L1=vL(VHKP0edge, VhK); //Line 33 The problem is here

```

But I get the following error:

```auto
  current line = 33
Assertion fail : (0)
	line :2764, in file problem.cpp
Assertion fail : (0)
	line :2764, in file problem.cpp
 err code 6 , mpirank 0

```

The problem comes from `matrix L1=vL(VHKP0edge, VhK)`.

It’s seems that I can not do 1D integration on this mesh. I don’t know what is the problem.

Could someone help me to understand what is the problem ? I have attached the two meshes used, to do some tests.

Thank you in advance,

Best regards,

Loïc,

---

<div class="post-metadata">

**Author:** ![Loic](https://avatars.discourse-cdn.com/v4/letter/l/e9c0ed/32.png) [@Loic](https://community.freefem.org/u/Loic)\
**Post date:** [March 7, 2022, 6:40am UTC](https://community.freefem.org/t/error-in-1d-integration/1554/4 "2022-03-07T06:40:09Z")

</div>

According to the documentation: **int1D()** does not support **meshS Type**.

I have solved my problem by converting my surface meshS into a 2D mesh.

Loïc,

---

<div class="post-metadata">

**Author:** ![frederichecht](https://yyz2.discourse-cdn.com/flex030/user_avatar/community.freefem.org/frederichecht/32/15_2.png) [@frederichecht](https://community.freefem.org/u/frederichecht)\
**Post date:** [March 7, 2022, 3:22pm UTC](https://community.freefem.org/t/error-in-1d-integration/1554/5 "2022-03-07T15:22:38Z")

</div>

Yes, I miss a piece of code, the simple way is the do in 2d, I will add in next version this peace of code .

THE CORRECTION /

```auto
MBP-M1-FH:ff-10 hecht$ git diff
diff --git a/src/fflib/problem.cpp b/src/fflib/problem.cpp
index 3d14aacd..b701f528 100755
--- a/src/fflib/problem.cpp
+++ b/src/fflib/problem.cpp
@@ -2760,13 +2760,14 @@ template<class R>
             }
         }
         else // int on edge ie
- //{
- ffassert(0);
- /*R2 PA,PB;
+ {
+ // ffassert(0);
+ R2 PA,PB;
             PA=TriangleHat[VerticesOfTriangularEdge[ie][0]];
             PB=TriangleHat[VerticesOfTriangularEdge[ie][1]];
             R3 E=T.Edge(ie);
             double le = sqrt((E,E));
+        
             for (npi=0;npi<FIb.n;npi++) // loop on the integration point
             {
                 QuadratureFormular1dPoint pi( FIb[npi]);
@@ -2865,7 +2866,7 @@ template<class R>
                             }
                     }
                 }}
- }*/
+ }
 
 
         *MeshPointStack(stack) = mp;
MBP-M1-FH:ff-10 hecht$ 

```