ROOT Version: 6.18/04
Platform: Ubuntu 19.10
Compiler:
g++ 4:9.2.1-3.1ubuntu1 amd64 GNU C++ compiler
Dear Root community,
I am currently trying to reproduce this paper DOI: 10.1137/S1064827500383123 but Root says that the matrix circ(0.5,0.25,0,…,0.25) is singular even though the determinant is >0 or for a 6x6 version of that matrix, the determinant is 33/2048~0.02. The precise error message is:
Error in TDecompLU::DecomposeLUCrout: matrix is singular
I get the same error for other circulant matrices and have cross checked with Print() that the matrices are written correctly:
| 0 | 1 | 2 | 3 | 4 |
----------------------------------------------------------------------
0 | 0.5 0.25 0 0 0
1 | 0.25 0.5 0.25 0 0
2 | 0 0.25 0.5 0.25 0
3 | 0 0 0.25 0.5 0.25
4 | 0 0 0 0.25 0.5
5 | 0.25 0 0 0 0.25
| 5 |
----------------------------------------------------------------------
0 | 0.25
1 | 0
2 | 0
3 | 0
4 | 0.25
5 | 0.5
In a past post it was suggested to scale the matrix beforehand, but this did not solve the issue for me.
I believe this might also be the reason why the FFT solution of the linear system of equations later fails, but I am not sure.
Can you help me with this please?
Thank you