[Sparse] Add a LADIES example

[xiangyuzhi]

Description

A LADIES model example use sparse library.

LADIES Algorithm:

Run example:

$ python examples/sparse/sampling/ladies.py
Training in gpu mode.
Loading data
[W TensorAdvancedIndexing.cpp:1615] Warning: scatter_reduce() is in beta and the API may change at any time. (function operator())
Training...
Epoch 00000 | Loss 2.8380 | Accuracy 0.5665 
Epoch 00001 | Loss 1.5582 | Accuracy 0.6852 
Epoch 00002 | Loss 1.2412 | Accuracy 0.7335 
Epoch 00003 | Loss 1.0939 | Accuracy 0.7564 
Epoch 00004 | Loss 1.0059 | Accuracy 0.7731 
Epoch 00005 | Loss 0.9572 | Accuracy 0.7796 
Epoch 00006 | Loss 0.9081 | Accuracy 0.7855 
Epoch 00007 | Loss 0.8707 | Accuracy 0.7935 
Epoch 00008 | Loss 0.8386 | Accuracy 0.7984 
Epoch 00009 | Loss 0.8159 | Accuracy 0.7994 
Epoch 00010 | Loss 0.7983 | Accuracy 0.8045 
Epoch 00011 | Loss 0.7795 | Accuracy 0.8060 
Epoch 00012 | Loss 0.7601 | Accuracy 0.8102 
Epoch 00013 | Loss 0.7465 | Accuracy 0.8119 
Epoch 00014 | Loss 0.7405 | Accuracy 0.8159 
Epoch 00015 | Loss 0.7234 | Accuracy 0.8197 
Epoch 00016 | Loss 0.7132 | Accuracy 0.8161 
Epoch 00017 | Loss 0.7117 | Accuracy 0.8223 
Epoch 00018 | Loss 0.6965 | Accuracy 0.8217 
Epoch 00019 | Loss 0.6871 | Accuracy 0.8237 
Testing...
Test accuracy 0.6383

Checklist

Please feel free to remove inapplicable items for your PR.

• The PR title starts with [$CATEGORY] (such as [NN], [Model], [Doc], [Feature]])
• I've leverage the tools to beautify the python and c++ code.
• The PR is complete and small, read the Google eng practice (CL equals to PR) to understand more about small PR. In DGL, we consider PRs with less than 200 lines of core code change are small (example, test and documentation could be exempted).
• All changes have test coverage
• Code is well-documented
• To the best of my knowledge, examples are either not affected by this change, or have been fixed to be compatible with this change
• Related issue is referred in this PR
• If the PR is for a new model/paper, I've updated the example index here.

Changes

[dgl-bot]

To trigger regression tests:

• @dgl-bot run [instance-type] [which tests] [compare-with-branch];
  For example: @dgl-bot run g4dn.4xlarge all dmlc/master or @dgl-bot run c5.9xlarge kernel,api dmlc/master

[dgl-bot]

Commit ID: af431adb3bc69bf6d1050a77190e9f13fa605ba6

Build ID: 1

Status: ✅ CI test succeeded.

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[dgl-bot]

Commit ID: 76a26340e540c32e0d4da6e2b56af5fedfcc682e

Build ID: 2

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[dgl-bot]

Commit ID: a08f25a6b4a93b6cdba39c8b28b02bc14707a6df

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Status: ❌ CI test failed in Stage [Torch GPU Example test].

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[xiangyuzhi]

@dgl-bot

[dgl-bot]

Commit ID: deccd6025d167e1dbbce22488db0cc0408abd42f

Build ID: 4

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[czkkkkkk]

@xiangyuzhi Please also include a figure of the pseudocode for LADIES in the description.

[dgl-bot]

Commit ID: 0ddbf1facd1744ba5eeb326f254b93344fdce3e9

Build ID: 5

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[dgl-bot]

Commit ID: 6c98567b576fe21094df1bfa5d6c44b724f4b6cf

Build ID: 6

Status: ✅ CI test succeeded.

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