Empty sparse matrix in SofaPython3 access_matrix bindings

[GaetanDesrues]

Problem

Description
I'm using SOFA v25.06 with SofaPython3 on ubuntu (WSL). I'm using python bindings to access system matrices as showcased in the examples (SofaPython examples). While it works for external forces and solution (b and x), I always end up with empty sparse matrices for system/mass/stiffness. In python scipy.sparse, I have nnz=0

Steps to reproduce
Build SOFA with SofaPython3 and run examples

Expected behavior
Non-empty system matrix

---

Environment

Context

• System: Ubuntu via WSL
• Version of SOFA: compiled from sources, SOFA&SofaPython3 v25.06

[GaetanDesrues]

@bakpaul

[bakpaul]

Hello !

I tried to launch the scene https://github.com/sofa-framework/SofaPython3/blob/master/examples/access_matrix.py on a freshly installed release from the binaries (those one exactly : https://github.com/sofa-framework/sofa/releases/download/v25.06.00/SOFA_v25.06.00_Linux-Python_3.12.zip).

On my side it shows

====================================
Global system matrix
====================================
dtype: float64
shape: (960, 960)
ndim: 2
nnz: 49537
====================================
System right hand side
====================================
dtype: float64
shape: (960,)
ndim: 1
====================================
System solution
====================================
dtype: float64
shape: (960,)
ndim: 1

Which means that it is a environment issue.
On my side I have :

• Ubuntu 24.04.2 (as main OS)
• python 3.12.3
• numpy 2.3.3
• scipy 1.16.2

Could you try with an equivalent environment ?

---> or maybe even easier, you could try to launch the binaries in your current env to see if it might be your compilation env that is in fault ?