Function distributed_cg 

pub fn distributed_cg<C: SolverCommunicator + ?Sized>(
    comm: &C,
    a: &DistributedCsr<'_>,
    b: &[f64],
    initial: Option<&[f64]>,
    jacobi: bool,
    options: CgOptions,
) -> Result<DistributedCgReport, SolverError>

Solve SPD A x=b with balanced contiguous row partitioning. optional Jacobi is local diagonal scaling. No checkpoint/restart inside a solve: an error aborts the communicator; create a fresh communicator before retrying.