It looks a bit sloppy to hardcode so many constants in a single file: `src/gauss_quadrature/legendre.rs`. Isn't it possible to generate them with the help of rust macros in the same way Julia uses metaprogramming?

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ok123456 10 months ago | parent | next [-]

Gaussian quadrature points are typically solved numerically. There's a good chance these ultimately came from a table.

Additionally, compile time floating-point evaluation is limited. When I looked around recently, I didn't see a rust equivalent of gcem; any kind of transcendental function evaluation (which finding Gaussian quadrature points absolutely would require) would not allow compile-time evaluation.

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AlotOfReading 10 months ago | parent | next [-]

Support for float const fns was merged just a couple months ago and hasn't been officially announced yet.

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BD103 10 months ago | parent | next [-]

Support for constant float operations was released in Rust 1.82! https://blog.rust-lang.org/2024/10/17/Rust-1.82.0.html

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ok123456 10 months ago | parent | prev [-]

IIRC, that only supports elementary arithmetic operations. Useful but not general.

	▲	AlotOfReading 10 months ago \| parent [-]
		It's relatively straightforward to build transcendental functions out of the basic operations and the stdlib support will eventually get there, but rust's float story is still a work in progress. They're trying to do things more properly and document semantics better than C and C++ have.

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zokier 10 months ago | parent | prev [-]

I was under the impression that macros can execute arbitrary code, surely some FP would not be big problem. And if not macros then build.rs script certainly could do the trick.

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dhosek 10 months ago | parent [-]

build.rs can definitely execute arbitrary code, which means that a lot of places (including, IIRC crates.io) will forbid crates that rely on build.rs. I ended up refactoring my build.rs into a separate sub-application in finl_unicode that built data tables which are then checked into git and used pre-built. I include the sub-app in the source code so that anyone with access to the repo could continue development if I were to die tomorrow.

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n_plus_1_acc 10 months ago | parent [-]

There are many crates with build.rs scripts on crates.io, because they host just the source code with the Cargo.{toml,lock}.

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dhosek 10 months ago | parent [-]

I ran into some issues with crates.io and my build.rs when I first released the crate, although it’s long enough ago, that I don’t remember exactly what the issue was. It might also have been that the build.rs script downloaded raw data files from unicode.org

	▲	Arnavion 10 months ago \| parent [-]
		crates.io doesn't care what your build.rs does because it doesn't try to compile your code, neither now or ever in the past. There would be no point in it trying to compile your code; there are lots of crates that are bindings to C libraries that crates.io's builders can't be expected to have, crates that target architectures which crates.io can't be expected to have builders for, etc.

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mtantaoui 10 months ago | parent | prev | next [-]

this was mainly to use an Iteration free method in this paper: https://www.cfm.brown.edu/faculty/gk/APMA2560/Handouts/GL_qu...

this method is much faster and simpler.

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two_handfuls 10 months ago | parent | prev [-]

Probably but that would slow down compilation a lot.

	▲	simlevesque 10 months ago \| parent \| next [-]
		Exactly, it's not like the constants are gonna change.
	▲	blharr 10 months ago \| parent \| prev \| next [-]
		You wouldn't have to recompile them every time. What if you didn't necessarily use macros but auto-generated it in a file that you keep separate from the other code at the bottom?
	▲	dataflow 10 months ago \| parent \| prev [-]
		What I would do in these cases is to define the general computation function, but special-case it to return the hard-coded value for specific common inputs if it's being evaluated at compile time. Then add a test to verify both behaviors.