UPDATE: Dump of initial files

base/src/functions/engineering/transcendental/README.md

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+# Creating tests from transcendental functions
+
+Excel supports a number of transcendental functions like the error functions, gamma nad beta functions.
+In this folder we have tests for the Bessel functions.
+Some other platform's implementations of those functions are remarkably poor (including Excel), sometimes failing on the third decimal digit. We strive to do better.
+
+To properly test you need to compute some known values with established arbitrary precision arithmetic.
+
+I use for this purpose Arb[1], created by the unrivalled Fredrik Johansson[2]. You might find some python bindings, but I use Julia's Nemo[3]:
+
+```julia
+julia> using Nemo
+julia> CC = AcbField(200)
+julia> besseli(CC("17"), CC("5.6"))
+```
+
+If you are new to Julia, just install Julia and in the Julia terminal run:
+
+```
+julia> using Pkg; Pkg.add("Nemo")
+```
+
+You only need to do that once (like the R philosophy)
+
+Will give you any Bessel function of any order (integer or not) of any value real or complex
+
+[1]: https://arblib.org/
+[2]: https://fredrikj.net/
+[3]: https://nemocas.github.io/Nemo.jl/latest/