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From "Dylan Hutchison (JIRA)" <>
Subject [jira] [Created] (SYSTEMML-1985) Sparsity estimates of constant multiply
Date Fri, 03 Nov 2017 04:54:00 GMT
Dylan Hutchison created SYSTEMML-1985:

             Summary: Sparsity estimates of constant multiply
                 Key: SYSTEMML-1985
             Project: SystemML
          Issue Type: Improvement
            Reporter: Dylan Hutchison
            Priority: Minor

I've seen the following in the output of Explain recompile_hops:

--(505) TRead HV [327,1,1000,1000,327] [0,0,0 -> 0MB], CP
--(37959) b(*) (505,[-0.0053168...]) [327,1,1000,1000,-1] [0,0,0 -> 0MB], CP

The nnz of Hop 37959 here is 327, because multiplying a matrix by a non-zero constant does
not change the non-zero structure.  But the current code marks the nnz as -1 (unknown nnz).

Let's add a check to the {{refreshSizeInformation}} of BinaryOp to handle this and related
cases like division by a nonzero.  

Addition, subtraction, and mod might create zeros so they are tricky; however we can upper
bound their nnz. Maybe this might be helpful in a different place?

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