# Abhijeet

N = 4 # N by N by N array of atoms 
# surrounding the N**3 atoms is another layer of invisible fixed-position atoms
# that provide stability to the lattice.
k = 1 
m = 1 
spacing = 1 
atom_radius = 0.3*spacing 
LO = spacing-1.8*atom_radius
VO = pi*(0.5*atom_radius)**2*LO # initial volume of spring
scene.center = 0.5*(N-1)*vector(1,1,1)
dt = 0.04*(2*pi*sqrt(m/k))
axes = [vector(1,0,0), vector(0,1,0), vector(0,0,1)]

scene.caption= """A model of a solid represented as atom connected by inter atomic bond.

To rotate "camera", drag with right button or ctrl-drag.
To zoom, drag with middle button or Alt/option depressed, or used scroll wheel.
  On a two-button mouse, middle is left + right.
To pan left/right and up/down, shift-drag.
Touch screen: pinch/extend to zoom, swipe or two-finger rotate."""
  
class crystal:
  
  def __init__(self, N, atom_radius, spacing, momentumRange):
      self.atoms = []
      self.spring = []
      
      # create (N+2)^3 atoms in a grid; the outermost atoms are fixed and invisible
      for z in range(-1,N+1,1):
        for y in range(-1,N+1,1):
          for x in range(-1,N+1,1):
            atom = sphere()
            atom.pos = vector(x,y,z)*spacing
            atom.radius = atom_radius
            atom.color = vector(0,0.58,0.69)
            if 0 <= x < N and 0 <= y < N and 0 <= z < N:
                p = vec.random()
                atom.momentum = momentumRange*p
            else:
              atom.visible = False
              atom.momentum = Vec(0,0,0)
            atom.index = len(self.atom)
            self.atoms.append( atom )
      for atom in self.atoms:
        if atom.visible:
          if atom.pos.x == 0:
            self.make_spring(self.atoms[atom.index+1], False)
            self.make_spring(atom, self.atoms[atom.index+1],True)
          elif atom.pos.x == N-1:
            self.make_spring(atom, self.atoms[atom.index+1], False)
          else:
            self.make_spring(atom, self.atoms[atom.index+1], True)
            
          if atom.pos.y == 0:
            self.make_spring(self.atom[atom.index-(N+2)], atom, False)
            self.make_spring(atom, self.atoms[atom.index+(N+2)],True)
          elif atom.pos.y == N-1:
            self.make_spring(atom, self.atoms[atom.index+(N+2)], False)
          else:
            self.make_spring(atom, self.atoms[atom.index+(N+2)], True)
            
          if atom.pos.z == 0:
            self.make_spring(self.atoms[atom.index-(N+2)**2], atom, False)
            self.make_spring(atom, self.atoms[atom.index+(N+2)**2],True)
          elif atom.pos.z == N-1:
            self.make_spring(atom, self.atoms[atom.index+(N+2)**2], False)
          else:
            self.make_spring(atom, self.atoms[atom.index+(N+2)**2], True)
            
  # Create a grid of spring linking each atom to the adjacent atoms
  # in each dimension, or to invisible motionless atoms
  def make_spring(self, start, end, visible):
      spring = helix()
      spring.pos = start.pos 
      spring.axis = end.pos-start.pos 
      spring.visible = visible
      spring.thickness = 0.05
      spring.radius = 0.5*atomic_radius
      spring.lenght = spacing
      spring.start = start
      spring.end = end
      spring.color = color.orange 
      self.springs.append(spring)
      
c = crystal(N, atom_radius, spacing, 0.1*spacing*sqrt(k/m))

while True:
  rate(60)
  for atom in c.atoms:
    if atom.visible:
        atom.pos = atom.pos + atom.momentum/m*dt
  for spring in c.springs:
    spring.axis = spring.end.pos - spring.start.pos 
    L = mag(spring.axis)
    spring.axis = spring.axis.norm()
    spring.pos = spring.start.pos+0.5*atom_radius*spring.axis
    Ls = L-atom_radius
    spring.lenght = Ls
    Fdt = spring.axis * (k*dt * (1-spacing/L))
    if spring.start.visible:
      spring.start.momentum = spring.start.momentum + Fdt
    if spring.end.visible:
      spring.end.momentum = spring.end.momentum - Fdt
       

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