Function solve_implicit_system 

pub fn solve_implicit_system(
    mat: &[Vec<f64>],
    rhs: &[f64],
) -> OptimizeResult<Vec<f64>>

Solve the linear system A x = rhs via Gaussian elimination with partial pivoting.

Both mat (square, row-major) and rhs are consumed / mutated.

Errors

Returns OptimizeError::ComputationError if the matrix is singular.