Added loss function and unit test for Poisson Loss

[yorozuya-2003]

References to other Issues or PRs or Relevant literature

Fixes #9

Brief description of what is fixed or changed

• Added class for Poisson Loss in \MLlib\loss_func.py
• Added unit test corresponding to the same in \MLlib\tests\test_loss_func.py

Other comments

The unit test approximately compares the output of the implemented loss function with that of the corresponding loss function already there in TensorFlow when using the same test example as input.

[codecov]

Codecov Report

Attention: Patch coverage is 83.33333% with 3 lines in your changes missing coverage. Please review.

Project coverage is 13.96%. Comparing base (f43f6e7) to head (7bce8a5).

Files with missing lines	Patch %	Lines
MLlib/loss_func.py	70.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #211      +/-   ##
==========================================
+ Coverage   11.56%   13.96%   +2.39%     
==========================================
  Files          31       32       +1     
  Lines        2438     2456      +18     
==========================================
+ Hits          282      343      +61     
+ Misses       2156     2113      -43     

Flag	Coverage Δ
unittests	13.96% <83.33%> (+2.39%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
MLlib/tests/test_loss_func.py	100.00% <100.00%> (ø)
MLlib/loss_func.py	44.53% <70.00%> (+44.53%)	⬆️

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[rohansingh9001]

The loss method and the unit test looks good to me however it will not really be useful if you did not add a derivative method like the other loss classes in this file. Without a derivative function, the framework's models are unable to utilize loss classes.

[rohansingh9001]

The derivative function is missing from Poison loss class.

[yorozuya-2003]

References to other Issues or PRs or Relevant literature

Fixes #9

Brief description of what is fixed or changed

• Added derivative method for PoissonLoss class in \MLlib\loss_func.py

Other comments

I have tried adding the derivative method for the Poison loss class. Please suggest any corrections required. Thank you.