Bonded.bond_fpair: def of bend-prot@0.1.0.0
Import: import bend-prot@0.1.0.0/bonded.bend as Bonded
Lines 266-272 of bend-prot@0.1.0.0/bonded.bend: https://jend.leeeet.dev/read.txt?path=bend-prot@0.1.0.0/bonded.bend&start_line=266&end_line=272

import Base
import bend-prot@0.1.0.0/geom.bend as G

# Bond forces: F = -2k(d-r0) * unit(pa-pb) on a, opposite on b; zero for
# coincident or missing atoms. Per-atom loop over flat bonds.
def bond_fpair(+d: G.Vec3, +d2: F32, +k: F32, +r0: F32) -> G.Vec3 & G.Vec3:
  +r = F32.sqrt(d2)
  +mag = Bool.pick(F32, F32.is_eq(d2, 0.0), 0.0, (((0.0 - (2.0 * k : F32) : F32) * (r - r0 : F32) : F32) / r : F32))
  +fa = G.Vec3.scale(mag, d)
  (fa, G.Vec3.neg(fa))

Uses (12):
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Bool.pick
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=F32
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=F32.div
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=F32.is_eq
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=F32.mul
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=F32.sqrt
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=F32.sub
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Pair
  https://jend.leeeet.dev/definition.txt?path=Base/base.bend&name=Sigma
  https://jend.leeeet.dev/definition.txt?path=bend-prot@0.1.0.0/geom.bend&name=Vec3
  https://jend.leeeet.dev/definition.txt?path=bend-prot@0.1.0.0/geom.bend&name=Vec3.neg
  https://jend.leeeet.dev/definition.txt?path=bend-prot@0.1.0.0/geom.bend&name=Vec3.scale