# UMFPACK WARNING singular matrix
**URL:** https://community.freefem.org/t/umfpack-warning-singular-matrix/3685
**Category:** General Discussion
**Created:** [January 11, 2025, 12:07am UTC](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685 "2025-01-11T00:07:29Z")
**Posts on this page:** 5
**Page:** 1
### Author:  [@bchen-00](https://community.freefem.org/u/bchen-00)
#### Post date: [January 11, 2025, 12:07am UTC](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685/1 "2025-01-11T00:07:29Z")
Hello,
I have compiled the FreeFEM++ code successfully using the source code on main branch, but cannot use it to solve any problem (even the ones in example) without encountering
" UMFPACK WARNING singular matrix "
This seems to only be a problem on a specific machine running Ubuntu 22.04, as I have been able to use FreeFEM++ without a problem on another machine running Ubuntu 20.04. Is there something wrong with my installation?
Thanks in advance,
Boyuan
---
### Author:  [@bchen-00](https://community.freefem.org/u/bchen-00)
#### Post date: [January 13, 2025, 7:29pm UTC](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685/2 "2025-01-13T19:29:07Z")
Sorry about the lack of information in the initial post. Both Machines are actually Ubuntu 22.04. The issue is specific to UMFPACK on one of them, but when I select the solver to be GMRES, it returns the expected result. More specifically, using the default solver for an example case gives
```auto
-- FreeFem++ v4.13 (Mon Jan 13 11:07:38 AM PST 2025 - git v4.13)
file : 2D-test.edp
Load: lg_fem lg_mesh lg_mesh3 eigenvalue
1 : // Parameters
2 : real theta = 4.*pi/3.;
3 : real a = 2.; //The length of the semimajor axis
4 : real b = 1.; //The length of the semiminor axis
5 : func z = x;
*** Warning The identifier z hide a Global identifier
6 :
7 : // Mesh
8 : border Gamma1(t=0., theta){x=a*cos(t); y=b*sin(t);}
9 : border Gamma2(t=theta, 2.*pi){x=a*cos(t); y=b*sin(t);}
10 : mesh Th = buildmesh(Gamma1(100) + Gamma2(50));
11 :
12 : // Fespace
13 : fespace Vh(Th, P2); //P2 conforming triangular FEM
14 : Vh phi, w, f=1;
15 :
16 : // Solve
17 : solve Laplace(phi, w)
18 : = int2d(Th)(
19 : dx(phi)*dx(w)
20 : + dy(phi)*dy(w)
21 : )
22 : - int2d(Th)(
23 : f*w
24 : )
25 : + on(Gamma1, phi=z)
26 : ;
27 :
28 : // Plot
29 : plot(phi, wait=true, ps="membrane.eps"); //Plot phi
30 : plot(Th, wait=true, ps="membraneTh.eps"); //Plot Th
31 :
32 : // Save mesh
33 : savemesh(Th,"Th.msh");
34 : sizestack + 1024 =1896 ( 872 )
-- mesh: Nb of Triangles = 2568, Nb of Vertices 1360
1 UMFPACK WARNING singular matrix
1 UMFPACK WARNING singular matrix
-- Solve :
min -nan max -nan
number of required edges : 0
times: compile 0.09037s, execution 2.72271s, mpirank:0
CodeAlloc : nb ptr 3866, size :515232 mpirank: 0
Ok: Normal End
```
But GMRES returns the expected outcome
```auto
-- FreeFem++ v4.13 (Mon Jan 13 11:07:38 AM PST 2025 - git v4.13)
file : 2D-test.edp
Load: lg_fem lg_mesh lg_mesh3 eigenvalue
1 : // Parameters
2 : real theta = 4.*pi/3.;
3 : real a = 2.; //The length of the semimajor axis
4 : real b = 1.; //The length of the semiminor axis
5 : func z = x;
*** Warning The identifier z hide a Global identifier
6 :
7 : // Mesh
8 : border Gamma1(t=0., theta){x=a*cos(t); y=b*sin(t);}
9 : border Gamma2(t=theta, 2.*pi){x=a*cos(t); y=b*sin(t);}
10 : mesh Th = buildmesh(Gamma1(100) + Gamma2(50));
11 :
12 : // Fespace
13 : fespace Vh(Th, P2); //P2 conforming triangular FEM
14 : Vh phi, w, f=1;
15 :
16 : // Solve
17 : solve Laplace(phi, w, solver=GMRES)
18 : = int2d(Th)(
19 : dx(phi)*dx(w)
20 : + dy(phi)*dy(w)
21 : )
22 : - int2d(Th)(
23 : f*w
24 : )
25 : + on(Gamma1, phi=z)
26 : ;
27 :
28 : // Plot
29 : plot(phi, wait=true, ps="membrane.eps"); //Plot phi
30 : plot(Th, wait=true, ps="membraneTh.eps"); //Plot Th
31 :
32 : // Save mesh
33 : savemesh(Th,"Th.msh");
34 : sizestack + 1024 =1896 ( 872 )
-- mesh: Nb of Triangles = 2568, Nb of Vertices 1360
** fgmres has converged in 325 iterations The relative residual is 9.93524e-07 Cl: 0.107376
-- Solve :
min -2 max 2
number of required edges : 0
times: compile 0.22081s, execution 1.77229s, mpirank:0
```
This issue is not present on another machine - does anyone has insights on what the issue might be?
---
### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [January 13, 2025, 9:31pm UTC](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685/3 "2025-01-13T21:31:30Z")
There is probably an issue with your installation.
I ran the code, and get on both macOS and Linux:
```auto
[...]
-- mesh: Nb of Triangles = 2568, Nb of Vertices 1360
-- Solve :
min -2 max 2
[...]
```
---
### Author:  [@bchen-00](https://community.freefem.org/u/bchen-00)
#### Post date: [January 14, 2025, 4:10am UTC](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685/4 "2025-01-14T04:10:37Z")
Do you know what could be the issue? I tried to reinstalling a few times in different ways and nothing changes.
---
### Author:  [@prj](https://community.freefem.org/u/prj)
#### Post date: [January 14, 2025, 6:18am UTC](https://community.freefem.org/t/umfpack-warning-singular-matrix/3685/5 "2025-01-14T06:18:25Z")
Did you install PETSc via `make petsc-slepc`?