[
https://issues.apache.org/jira/browse/SYSTEMML-220?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15427124#comment-15427124
]
Mike Dusenberry commented on SYSTEMML-220:
------------------------------------------
[~deron] No I don't believe they were ever created.
> New Second-Order Builtin Function 'apply'
> -----------------------------------------
>
> Key: SYSTEMML-220
> URL: https://issues.apache.org/jira/browse/SYSTEMML-220
> Project: SystemML
> Issue Type: Task
> Components: Compiler, Parser, Runtime
> Reporter: Matthias Boehm
> Original Estimate: 160h
> Remaining Estimate: 160h
>
> In several scripts, there is a need to apply rather complex functions to each
> cell of a matrix. The most natural way of expressing that, especially if this
> function involves loops and branches, are DML-bodied functions over scalars
> and surrounding loops over all cells in the matrix. Below is an artificial
> example:
> {code}
> foo = function( Double in ) return ( Double out ){
> x = in^2;
> if( x > in*2 )
> x = x - in/3;
> out = x + 7;
> }
> R = matrix(0, rows=nrow(A), cols=ncol(A));
> for( i in 1:nrow(A) )
> for( j in 1:ncol(A) )
> R[i,j] = foo(A[i,j])
> {code}
> Especially, on large data, this would however cause severe performance
> problems. Accordingly, people usually "vectorize" these operations by hand
> which is unfortunately not too easy for very complex functions.
> {code}
> R = A^2 - ppred(A^2, A*2, ">")*A/3 + 7;
> {code}
> For this reason, we would like to integrate a second-order builtin function
> {{apply}} that would allow users to use their custom functions with
> reasonable performance.
> {code}
> R = apply(A, foo);
> {code}
> We would initially constraint this builtin function to DML-bodied functions
> with (1) single scalar in / single scalar out, (2) no support for nested
> function invocations, (3) no creation of arbitrarily large intermediates (we
> assume small memory footprint per cell). These constraints would allow us to
> provide a very efficient new unary apply operation (multi-threaded in CP,
> narrow transformation in distributed backends).
--
This message was sent by Atlassian JIRA
(v6.3.4#6332)
