Matthias Boehm created SYSTEMML-2173:

             Summary: Upper bound nnz propagation over spark instructions
                 Key: SYSTEMML-2173
             Project: SystemML
          Issue Type: Bug
            Reporter: Matthias Boehm

Due to lazy evaluation, many spark instructions propagate nnz only if they can 
be exactly inferred from the input meta data. Especially for ultra-sparse 
matrices this poses a challenge because intermediates quickly reach a state 
where they're assumed to be dense. However, many operations such as right 
indexing allow to upper bound the nnz with the nnz in the input, which can be 
propagated and exploited in subsequent instructions.

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