[ohno]

Closes #39.

Summary

Add the three requested hadron spectroscopy examples to the Gaussian Expansion Method documentation:

• Lambda_c(1/2+) using the Kim, Hiyama, Oka, and Suzuki parameters.
• eta_c(1S) using the Meng, Wang, and Oka AL1 parameters.
• eta_c(1S) using the Arifi, Happ, Ohno, and Oka semirelativistic parameters.

Document each Hamiltonian, natural units, spin factors, and the role of RestEnergy with RelativisticKinetic. Preserve the parameters, basis ranges, executable examples, and three regression tests from the existing draft. Move the examples from the Rayleigh–Ritz page to GEM, as requested in the issue.

The calculated masses are 2286.000, 3005.252, and 3020.148 MeV. Explicitly document that the Arifi example differs from the issue's quoted 3019 MeV by about 1.15 MeV; the reference-comparison tolerances do not establish numerical convergence.

Validation

• All three executable example blocks are unchanged from the previous draft commit bae293a, whose CI passed.
• Patch application and the move of all three example blocks were checked locally.
• Julia is unavailable in the current local environment; the updated documentation and package tests are being checked by GitHub Actions.

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The original implementation was developed with assistance from Codex using GPT-5.6 Sol. The GEM documentation follow-up was also prepared with Codex assistance.

[MartinMikkelsen]

Also done here

[ohno]

@MartinMikkelsen
I added more and better examples
#39 (comment)

I will also have this pull request fixed.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.

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