random_conf

#!/usr/bin/env python
# write coordinates for a random configuration.
import numpy as np
import os
import sys
from math import pi as M_PI
from math import sqrt

N = 100
rho = .25

argc = len (sys.argv)
i = 1
while i < argc:
    if sys.argv[i] == 'eta':
        rho = float (sys.argv[i+1]) / M_PI
        i += 2
    elif sys.argv[i] == 'rho':
        rho = float (sys.argv[i+1])
        i += 2
    elif sys.argv[i] == 'dee':
        dee = float (sys.argv[i+1])
        i += 2
        rho = 1. / M_PI / dee / dee
        del dee
    elif sys.argv[i] == 'N':
        N = int (sys.argv[i+1])
        i += 2
    elif sys.argv[i] == 'seed':
        seed = int (sys.argv[i+1])
        np.random.seed (seed)
        i += 2
    elif sys.argv[i] == '-C':
        os.chdir (sys.argv[i+1])
        i += 2
    else:
        abort ("Nope")

def square_lattice (ncells, rho):
    """
    construct a perfect square lattice with approximately
    N particles, and precise number density rho.
    returns (coordinates, slack, box vectors)
    """
    N = ncells
    A = N / rho
    L = np.sqrt (A)
    L = [ L, L ]
    slack = 0
    eta_unit_disks = M_PI * rho  # assume unit disks
    dee = (M_PI*rho)**-.5
    print "actual parameters:", locals ()

    XX = np.random.random (size=N) * L[0]
    YY = np.random.random (size=N) * L[1]

    coords = np.transpose ([XX, YY])

    return coords, slack, L

coords, slack, L = square_lattice (N, rho)
N = len (coords)
L = np.array (L)

# canonicalize coordinates into [0; L)
coords += L
coords %= L

mini = np.min (coords, axis=0)
maxi = np.max (coords, axis=0)
assert np.all (mini >= 0.)
assert np.all (maxi < L)

np.savetxt ("coords.dat", coords)
np.savetxt ("periods", (L[0], L[1], 0.))