wehub-resource-sync
76 lines
3.3 KiB
Markdown
76 lines
3.3 KiB
Markdown
# Create View
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## Status
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**Discussion**
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Proposed by: Adam Gibson (27th April 2022)
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Discussed with: Paul Dubs
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Finalized by: Adam Gibson (5th May 2022)
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## Context
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Samediff's op graph mainly focuses on immutability to prevent bugs making many variable inputs and outputs for various ops copy on write.
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This prevents performance gains with in place ops such as +=.
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Currently, the samediff strided_slice operation works to provide a view of an array
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but the view is a copy. This limitation prevents performance gains you typically see in views.
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## Decision
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CreateView is an op that takes in a set of SDVariables that represents index information similar to nd4j's point, interval,all, and new axis. This op allows for dynamic generation of views of variables.
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CreateView is a building block for other ops to execute in place operations. Usage of CreateView should be deliberate and only used in certain circumstances.
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CreateView simply (using the aforementioned index inputs) creates a view using the existing data buffer and returns an output that wraps the same exact buffer as is rendered as an alternative view in a similar way as nd4j's indexing mechanisms.
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These inputs are represented as follows:
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1. Interval: INTERVAL_TYPE,2,1,start,end,stride,inclusive
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2. Point: POINT_TYPE,1,1,offset, DEFAULT_INCLUSIVE
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3. All: ALL_TYPE,0,1, DEFAULT_INCLUSIVE
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4. New Axis: NEW_AXIS,1,10, DEFAULT_INCLUSIVE
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This describes the general pattern the above described buffers follow:
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1. type of index
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2. Number of indices (representing offsets)
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3. Stride
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4. Inclusive/exclusive
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Of note here are a few constants representing types to be passed to the ops:
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1. *_TYPE: a pre-defined constant representing the kind of index this is
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2. DEFAULT_INCLUSIVE: whether the index's end is inclusive or not (only needed for intervals)
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this is by default 0 most of the time since the value is only relevant for intervals.
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These are created as INT64 ndarrays passed in to the
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operation itself.
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An omission of indexing here is SpecifiedIndex. Since SpecifiedIndex requires a copy most of the time, this op will mainly be focused on indexing that is guaranteed to use the same buffer.
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## In place exception in gradient checks
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Usually, arrays during training should not modify their outputs. Instead, new output arrays are allocated with calculated results being inserted into these pre-defined outputs.
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However, CreateView is, by definition, special since it is a building block for enabling manipulation of a view of the same data buffer as the input. The gradient checks in the [NonInplaceValidationListener](https://github.com/eclipse/deeplearning4j/blob/master/nd4j/nd4j-backends/nd4j-api-parent/nd4j-api/src/main/java/org/nd4j/autodiff/validation/listeners/NonInplaceValidationListener.java#L43) make an exception to this rule to account for this particular behaviour.
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## Consequences
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### Advantages
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* Self contained op for creating a view leveraging nd4j's existing indexing engine but
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better integrated as a libnd4j op allowing for better dynamic indexing of arrays
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* Similar in usage to indexes
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* Contains the potential bugs from views to a pre-specified op
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### Disadvantages
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* Could introduce new bugs upon use
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* Not the easiest interface requiring some constant methods
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* Not fully integrated in to the main engine/not as transparent as a tool as it should be |