Added Fresnel integrals #398

[curio-sitas]

Added Fresnel integrals from https://github.com/kiranshila/FresnelIntegrals.jl. As suggested in #398

Added 3 functions with docs :

• Fresnelc(z)
• Fresnels(z)
• Fresnnel(z) = (Fresnelc(z),Fresnels(z))

Tests were added too

[codecov]

Codecov Report

Merging #407 (08ed9e9) into master (36c547b) will increase coverage by 0.12%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #407      +/-   ##
==========================================
+ Coverage   93.63%   93.76%   +0.12%     
==========================================
  Files          12       13       +1     
  Lines        2767     2822      +55     
==========================================
+ Hits         2591     2646      +55     
  Misses        176      176              

Flag	Coverage Δ
unittests	93.76% <100.00%> (+0.12%)	⬆️

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

Impacted Files	Coverage Δ
src/SpecialFunctions.jl	100.00% <ø> (ø)
src/fresnel.jl	100.00% <100.00%> (ø)

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[curio-sitas]

Added the last test for the function fresnel(z::Number) for full code coverage (codecov)

[devmotion]

Thanks for the PR!

Unfortunately, I'm not sure if it will be merged since we have been hesitant with adding functionality to SpecialFunctions that already exists in other packages. Also here one could just load FresnelIntegrals, and it seems it's not necessary to include these functions in SpecialFunctions.

Nevertheless, I added comments and suggested some improvements. Even if this PR is not merged it might be useful to contribute those to FresnelIntegrals.

[curio-sitas]

Thanks for the review. I used to think it was a good idea to enrich the current package since it is a global SpecialFunctions collection.

I will take your reviews into account in my next commit and may open a PR on the original repo.

[curio-sitas]

• Sign errors were corrected and some tests added (comparison with QuadGK.jl).

All above is also proposed in a PR on the original repo (FresnelIntegrals.jl).

[devmotion]

@curio-sitas I guess this PR can be closed now since the PR in FresnelIntegrals.jl was merged and released in version 0.2?

[curio-sitas]

Yes you can close it !