modify generate_hafnian_sample to renormalize probabilities

[soranjh]

Context: This PR modifies the generate_hafnian_sample function by renormalizing probabilities. The sum of the computed probabilities in this function is sometimes slightly larger than 1.0 which leads to an error in generating random samples with numpy.random.choice. This error prevents simulating the vibronic properties of large molecules.

Description of the Change: The if statement in line 157 of samples.py is removed such that the probabilities are always renormalized if their sum is larger than 1.0.

Related GitHub Issues: https://github.com/XanaduAI/strawberryfields/issues/597

[codecov[bot]]

Codecov Report

Merging #250 (b4165e2) into master (e32c40a) will not change coverage. The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master      #250   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           21        21           
  Lines         1294      1293    -1     
=========================================
- Hits          1294      1293    -1     

Impacted Files	Coverage Δ
thewalrus/samples.py	100.00% <100.00%> (ø)

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[nquesada]

Thanks @soranjh : can you confirm that when you do this change the user who made the issue in SF stops getting errors?

[soranjh]

Thanks @soranjh : can you confirm that when you do this change the user who made the issue in SF stops getting errors?

Yes. The error disappears for one example.