[jira] [Updated] (SYSTEMML-1389) Update API: Pass in all outputs from `forward` to `backward` for performance

["Mike Dusenberry (JIRA)" <ji...@apache.org>]

     [ https://issues.apache.org/jira/browse/SYSTEMML-1389?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel ]

Mike Dusenberry updated SYSTEMML-1389:
--------------------------------------
    Issue Type: Improvement  (was: Sub-task)
        Parent:     (was: SYSTEMML-618)

> Update API: Pass in all outputs from `forward` to `backward` for performance
> ----------------------------------------------------------------------------
>
>                 Key: SYSTEMML-1389
>                 URL: https://issues.apache.org/jira/browse/SYSTEMML-1389
>             Project: SystemML
>          Issue Type: Improvement
>            Reporter: Mike Dusenberry
>            Assignee: Mike Dusenberry
>              Labels: SYSTEMML-618
>
> Currently, we do not pass the outputs of the {{forward}} functions to the {{backward}} functions in the {{nn}} library.  This aims to update the {{backward}} API to include (1) all relevant gradients from upstream, (2) *all* outputs from {{forward}}, and (3) *all* inputs given to {{forward}}.  Effectively, this would be equivalent to having a class object that maintains all configuration and input + output tensors.  If we had an object oriented design, most of the parameters to `forward` and `backward` would just be instance variables and thus would be accessible by `forward` or `backward` as needed.  Given that we don't have that design, this API update mimics that by allowing `backward` to have access to any inputs available to `forward`, as well as any outputs produced by `forward`.  This provides two benefits: first, many layers can benefit from a performance perspective from having access to the outputs of the {{forward}} function within the {{backward}} function, and second, this makes the API much simpler and less error prone by allowing for simple copy-and-paste of forward inputs and outputs as arguments to {{backward}} and by removing ambiguity related to the parameters.  A downside is that often times, not every single parameter is needed by {{backward}}.



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