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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