Codecov Report

Attention: Patch coverage is 97.99555% with 9 lines in your changes missing coverage. Please review.

Project coverage is 96.51%. Comparing base (bd9dc3e) to head (2926042).

@@            Coverage Diff             @@
##             main     #292      +/-   ##
==========================================
+ Coverage   96.38%   96.51%   +0.12%     
==========================================
  Files         184      190       +6     
  Lines        5152     5601     +449     
  Branches     1147     1214      +67     
==========================================
+ Hits         4966     5406     +440     
- Misses        186      195       +9     

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reading again the code, the operation with lambda = 1 of lambda D^TD where D is the derivative of the identity matrix, with 10 rows

 [
    [1, 0, 0, 0, 0, 0, 0, 0, 0, 0],
    [-1, 2, 0, 0, 0, 0, 0, 0, 0, 0],
    [0, -1, 2, 0, 0, 0, 0, 0, 0, 0],
    [0, 0, -1, 2, 0, 0, 0, 0, 0, 0],
    [0, 0, 0, -1, 2, 0, 0, 0, 0, 0],
    [0, 0, 0, 0, -1, 2, 0, 0, 0, 0],
    [0, 0, 0, 0, 0, -1, 2, 0, 0, 0],
    [0, 0, 0, 0, 0, 0, -1, 2, 0, 0],
    [0, 0, 0, 0, 0, 0, 0, -1, 2, 0],
    [0, 0, 0, 0, 0, 0, 0, 0, -1, 1],
  ];

It is a populated matrix of 10x10 by the indexes returned by createSystemMatrix, so it is already a lower triangular matrix.
I found:

• the bandwidth is the minimal so the cuthill-mckee permutations is not needed.
• the code of cholesky solver expect a upper triangular matrix instead of the lower triangular generated.