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https://issues.apache.org/jira/browse/SYSTEMML-2168?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16385399#comment-16385399
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Matthias Boehm commented on SYSTEMML-2168:
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[~lahiru94] thanks for your interest - this task here might be a good starting
point for you as it is well-isolated but will get you in touch with the
compiler of SystemML.
> New rewrite for removal of unnecessary right indexing
> -----------------------------------------------------
>
> Key: SYSTEMML-2168
> URL: https://issues.apache.org/jira/browse/SYSTEMML-2168
> Project: SystemML
> Issue Type: Task
> Reporter: Matthias Boehm
> Priority: Major
> Labels: beginner
>
> In several algorithms like {{scripts/algorithms/GLM-predict.dml}}, we see
> unnecessary right indexing operations that are not yet automatically removed.
> For example, in the following script
> {code}
> y_prob [, 1] = exp (linear_terms);
> y_prob [, 2] = 1.0 - y_prob [, 1];
> {code}
> the second access to {{y_prob [, 1]}} causes an unnecessary indexing
> operation and intermediate. We should rewrite this pattern to directly
> consume the output from {{exp (linear_terms)}} instead.
> In detail, this task entails the following steps, which might be a good
> opportunity to get in touch with SystemML's internal representation of
> high-level operators:
> * Create a new test case for this rewrite in package
> {{org.apache.sysml.test.integration.functions.misc}} similar to other test
> classes prefixed with {{Rewrite*}}.
> * Add a new rewrite to {{RewriteAlgebraicSimplificationDynamic}} to recognize
> the pattern of {{Indexing(LeftIndexing(X, y, indexrange1),indexrange2)}} with
> {{indexrange1==indexrange2}} and rewrite this to {{y}}. Note that there is a
> rewrite that replaces two subsequent leftindexing operations with an append,
> so this new rewrite should be invoked before
> {{fuseLeftIndexingChainToAppend}}.
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