bessel-via-amos.js

This is a very hastily-put-together library to export Scipy's kv and kve functions (modified Bessel functions of the second kind) to JavaScript/Node via WebAssembly.

The Scipy functions call a public domain Fortran library called AMOS, which were converted to C via f2c, which were then transpiled to WebAssembly via Emscripten.

This library adds some light library sugar around AMOS to give export a Scipy-like syntax.

Note: although AMOS and Scipy both operate on arrays of inputs, this library only exports JavaScript to handle scalar inputs because I can't figure out how to make Emscripten call AMOS' ZBESK routine fully. This is very much a proof-of-concept and AMOS deserves to be brought fully into WebAssembly (not just these two functions), and hopefully this library can help towards that goal.

Installation

npm i bessel-via-amos.js

Usage

TypeScript:

import amosPromise from 'bessel-via-amos.js';
(async function main() {
  const amos = await amosPromise;
  console.log(amos.kve(4.4, 3.3));
})();

Browser: I'm not sure but it hopefully won't be hard.

Dev

Diary of how I made this.

First set up miniconda, then

conda create -n amos-env
conda activate amos-env
conda install -c conda-forge f2c # might need more things

Now get AMOS, via Scipy.

git clone https://github.com/scipy/scipy.git --depth=1
cp -pr scipy/scipy/special/amos .
cd amos

curl -LO http://www.netlib.org/blas/i1mach.f 
curl -LO http://www.netlib.org/blas/r1mach.f
curl -LO http://www.netlib.org/blas/d1mach.f 

f2c *f

export CONDA_TOP_LEVEL=`conda info --envs | grep '*' | awk '{print $NF}'`

gcc -lf2c -L $CONDA_TOP_LEVEL/lib  -I $CONDA_TOP_LEVEL/include *c -o main
DYLD_LIBRARY_PATH=$CONDA_TOP_LEVEL/lib ./main

For emscripten, first install Emscripten and activate emsdk. Then

git clone https://github.com/gergondet/libf2c-emscripten
cd libf2c-emscripten
make -j4
cp f2c.h libf2c.a /PATH/TO/amos-js/amos

I haven't bundled these because likely as emsdk advances, these files will change?

Then back in amos, ensuring that emsdk is installed and activated,

emcc -lm -lf2c -L. *c

Confirm this runs and outputs something like cyr=7.443113:

node a.out.js

Now to make a library:

emcc -Os -lm -lf2c -L. -sMODULARIZE -sEXPORTED_FUNCTIONS=_kve,_kv,_zbesk_ *c

Now

cp a.out.* ../

And run node demo.js and confirm that it prints out 7.44311267732952.