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Date: Wed, 24 May 2017 06:42:04 +0000 (UTC)
From: "Nakul Jindal (JIRA)" <jira@apache.org>
To: issues@systemml.incubator.apache.org
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Subject: [jira] [Commented] (SYSTEMML-1570) Remove fused sel+ operator
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archived-at: Wed, 24 May 2017 06:42:08 -0000


    [ https://issues.apache.org/jira/browse/SYSTEMML-1570?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16022385#comment-16022385 ] 

Nakul Jindal commented on SYSTEMML-1570:
----------------------------------------

[~mboehm7] - absolutely. We haven't yet seen it as a top heavy hitter that we wanted to focus on, so it hasn't been implemented yet. 
If you think this is urgent, let me know and I can work on it.


> Remove fused sel+ operator
> --------------------------
>
>                 Key: SYSTEMML-1570
>                 URL: https://issues.apache.org/jira/browse/SYSTEMML-1570
>             Project: SystemML
>          Issue Type: Task
>            Reporter: Matthias Boehm
>             Fix For: SystemML 1.0
>
>
> The fused operator sel+ (select positive values) is applied for patterns like (X>0)*X and max(X,0) in order to eliminate unnecessary intermediates. It stems from a time when max was sparse-unsafe and hence inefficient over sparse data. However, meanwhile we mark scalar operators as conditionally sparse-safe depending on the given scalar constant c, which applies for max if c<=0. Hence, this sel+ operator is meanwhile completely useless and should be removed.
> Furthermore, we should also generalize the rewrites to rewrite the selection of negative values (X<0)*X to min(X,0)


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