[eigen] Checking if a dense linear system is solvable? |

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Hi,
unfortunately, the dense linear solvers don't have an .info() method.
Invoked with a singular matrix I just get "+-inf".
Checking the determinant isn't an option since, e.g.,

`0.1*IdentyMatrix(100,100) has a determinant of 1E-100 although it has
``only a condition number of 100.
`

`I suggest one either adds an info-method or one returns a vector
``(matrix) with zero rows.
`
What do think about that.

`Probably, the solve method should have an additional parameter with a
``sensible default,
``giving a (relative) tolerance for deciding if a pivot element has to be
``considered as zero.
`
Helmut.