[ https://issues.apache.org/jira/browse/SYSTEMML1678?page=com.atlassian.jira.plugin.system.issuetabpanels:alltabpanel
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Mike Dusenberry updated SYSTEMML1678:

Issue Type: New Feature (was: Subtask)
Parent: (was: SYSTEMML618)
> Add new 1D top_k utility function
> 
>
> Key: SYSTEMML1678
> URL: https://issues.apache.org/jira/browse/SYSTEMML1678
> Project: SystemML
> Issue Type: New Feature
> Reporter: Mike Dusenberry
> Assignee: Fei Hu
> Labels: SYSTEMML618
> Fix For: SystemML 1.0
>
>
> We should add new {{top_k}} and {{top_k2d}} utility functions (in {{nn/util.dml}}) that
accept a matrix {{X}} and return matrices {{values}} and {{indices}} with the top {{k}} values
(i.e. probabilities) and associated indices (i.e. classes) along a certain dimension. This
will be modeled after the [{{top_k}} function in TensorFlow  https://www.tensorflow.org/api_docs/python/tf/nn/top_k]
For the 1D case, {{top_k}} will operate on the columns dimension. A typical use case is
that in which {{X}} is the output of a {{softmax}} layer (so each row contains a set of normalized
class probabilities), and {{values}} and {{indices}} will contain rows with the top {{k}}
probabilities and class indices as described above. For the 2D case, {{top_k}} will operate
on the channels dimension. A typical use case here is that in which {{X}} is the output of
a {{softmax2d}} layer (so each channel contains a set of normalized class probabilities),
and {{values}} and {{indices}} will contain the top {{k}} probabilities and indices along
the channel axis. This scenario would be common in an image segmentation problem, in which
every pixel of the output image will have a set of class probabilities along the channel axis.
> Having these {{topk}} functions will allow us to extract either predict a single class
for each item, or the top {{k}} classes, and therefore may be more useful that a {{predict_class}}
function.
> Although we will use {{values}} and {{indices}} as the names of the returned matrices
within the functions, in practice, one is likely to name the results {{probs}} and {{classes}}
in the calling environment.

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