Function sddmm_preprocess 

pub fn sddmm_preprocess<T: SparseScalar>(
    handle: &Handle,
    op_a: Op,
    op_b: Op,
    alpha: &T,
    a: &DnMat<'_, T>,
    b: &DnMat<'_, T>,
    beta: &T,
    c: &mut SpMat<'_, T>,
    alg: SDDMMAlg,
    workspace: &mut DeviceBuffer<u8>,
) -> Result<()>

One-time preprocessing before sddmm. See spmm_preprocess for the rationale.