Fix duplicate cost function calls in optimize() implementations

[danielcorreia96]

Description

Fixed duplicate cost function calls in optimize() implementations using a swarm pbest_cost initialization to np.inf.

Related Issue

Resolves: #257

Motivation and Context

As pointed out in #257, for each iteration of the algorithm, the cost function is being called twice in the current implementations. This leads to significant performance drawbacks in situations where the cost function is expensive to calculate.

Hence, we can just initialize the pbest_cost to np.inf in order to remove the second cost function call.

Full credits to @pdiaz2 for raising the issue and proposing this solution: I simply extracted the relevant changes from the solution provided via file (#257 (comment))

How Has This Been Tested?

1. Ran tests locally
2. Personal project

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.
• All new and existing tests passed.

Questions

• Not sure if this PR requires changes in the documentation
• Not sure if the code style is correct: I only ran "black pyswarms tests" before opening this PR (which formatted some files unrelated to the actual changes...)

[ljvmiranda921]

Hey @whzup , wanna help me out reviewing this one?

[whzup]

I think that's a good solution. Seems like we had some redundancies there. Although, @ljvmiranda921 do you want this to go straight into the master branch?

[ljvmiranda921]

Hi @whzup ! Yes, I think we can treat this as a bugfix and release immediately. OK, I'll leave this to your judgement. If you're fine with this then I'll make the merge to master

[whzup]

@ljvmiranda921 I think this works as it is, the tests run without errors so let us merge it 😄

[ljvmiranda921]

@whzup ok then! will merge this now and do a patch release

[ljvmiranda921]

@all-contributors please add @danielcorreia96 for bug and code

[allcontributors]

@ljvmiranda921

I've put up a pull request to add @danielcorreia96! 🎉

[ljvmiranda921]

@all-contributors please add @whzup for code, infrastructure, doc, and ideas

[allcontributors]

@ljvmiranda921

I've put up a pull request to add @whzup! 🎉