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## [ff3d-users] solve problem with choleski preconditioner

 From: Fedechicco Subject: [ff3d-users] solve problem with choleski preconditioner Date: Wed, 11 Nov 2009 17:24:49 +0100

```Hello,
I have some problems in extending the navier-stokes example: I wanted
to simulate a round tube with an obstacle instead of a
square-sectioned tube.
I managed to write a suitable POV file and I loaded it.
Then I tried to use it, but it fails on this section:

<------- code --------->
solve(v) in Omega by M

krylov(type=cg,precond=ichol)

{

pde(v)

= ((1/dt)*convect([u0,v0,w0],dt,v0) - dy(p0));

v = 0 on <1,0,0>;

v = 0 on M xmin;

};
<------- end code --------->

and if I change the precondictioner from ichol to diagonal it works.
I had this problem on windows as well on linux.

This is some output with verbosity 10:

<----- output --------->
========== Navier-Stokes step 1
Setting krylov::precond to ichol
Setting krylov::type to cg
* algebraic simplification of -mu
* algebraic simplification of --0.1
Solving Problem:

Unknowns: [u:P1]
Problem:
pde(u):
((100*convect([u0,v0,w0],0.01,u0))-dx(p0))
u = uin{uin} on 0
u = 0 on (1,0,0)

Using FEM fictitious domain discretization:
Method:  Elimination
Adding Characteristic function of the domain to PDEs
Computing degrees of freedom positions...
- number of degrees of freedom positions: 3969
Computing degrees of freedom positions: done
* algebraic simplification of 0.1 * {fem-P0}
Adding Characteristic function of the domain to PDEs: done
Using 4999 DOF over 5000 available!
Fictitious domain method: discretization...
- assembling matrix
- assembling matrix: done [cost: time: 1s - CPU time: 0.15s]
- assembling second member
Starting connectivity builder
- building face to cells mapping...
- FacesBuilder: building...
- FacesBuilder: done
done
- Storing cell to cells connectivity
Connectivity builder finished
- assembling second member: done [cost: time: 0s - CPU time: 0.13s]
- discretizing boundary conditions
Generating Surface Meshes
Starting connectivity builder
- Storing cell to edges connectivity
- EdgesBuilder: building...
- EdgesBuilder: done
Connectivity builder finished
Marching tetrahedra
Marching tetrahedra: done
Marching cube sur 0x4758ba0
Sets 1 References
nb tot vertices 4958
nb tot cells 9868
- second member modification
./BoundaryConditionDiscretizationElimination.hpp:76
########################################################
Implementation not finished! use of dofPosition required
########################################################
./BoundaryConditionDiscretizationElimination.hpp:76
########################################################
Implementation not finished! use of dofPosition required
########################################################
- matrix modification
Fictitious domain method: discretization done
- matrix copy time: time: 0s - CPU time: 0.08s
Krylov solver
- number of unknowns: 4999
- preconditioner: incomplete Choleski factorization
- preconditioner initialization

SparseMatrix.hpp:265:
cannot access element (8,8)

UNEXPECTED ERROR: this should not occure, please report it
<----- output --------->

I hope this can help,
sincerely
Federico

```