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From "Matthias Boehm (JIRA)" <j...@apache.org>
Subject [jira] [Created] (SYSTEMML-2168) New rewrite for removal of unnecessary right indexing
Date Sun, 04 Mar 2018 21:33:00 GMT
Matthias Boehm created SYSTEMML-2168:
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             Summary: 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


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 operations 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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