source/check_harmonic.cjs

const assert=require('node:assert/strict');
const {harmonicCoordinates}=require('../web/solver.js');
// One mass-normalized oscillator: analytical complex response F/(k-w²+i*w*c).
for(const f of [0,5,10,20])for(const c of [0,10,100]){
 const f0=10,zeta=.02,F=100,w=2*Math.PI*f,k=(2*Math.PI*f0)**2;
 const r=harmonicCoordinates([f0],[1],[F],c,zeta,f),a=k-w*w,b=w*(c+2*zeta*Math.sqrt(k)),den=a*a+b*b;
 assert.ok(Math.abs(r.real[0]-F*a/den)<1e-10);assert.ok(Math.abs(r.imag[0]+F*b/den)<1e-10);
 const twice=harmonicCoordinates([f0],[1],[2*F],c,zeta,f);assert.ok(Math.abs(twice.real[0]-2*r.real[0])<1e-10);
}
console.log('Analytical oscillator, resonance, zero-frequency limit and force scaling passed.');